Loss of Identity

""You say you don't have any objectives? That's tragic, you know, but you are still confused. The fact that you are empty means that you can fill that emptiness with as much as you want. You happy person, where's a better future than that?""

- Touko, Kara no Kyoukai:

What defines "you"? The concept of identity, never mind the search for it, is a complicated question that fiction tries to answer. Beware though, fiction likes to throw us curve balls.

Is it your memories? Those can be removed or altered. (Oh, are there ever so many ways.) How about your personality? Well, that changes over time naturally like it or not, but then again you can play someone else and find you like being them better. Is it your body? Less luck there, if it isn't a body swap it's a gender swap or something much worse. Does the Soul have anything to do with this? Are you still "you" if you reincarnate?

Then again, most of the previous changes are negative, but what about positive alterations? Flowers for Algernon Syndrome and What Measure Is a Non Super make you wonder just how valuable you are when you gain... or lose... faculties. The Mind Is a Plaything of the Body, after all.

Don't let our meandering college philosophy depress you. After all, every non-nerve cell in your body is replaced in seven years (some die and get replaced, some go through mitosis and divide into two... wait, would that make those the same cell or two new ones? Does the original count as dead after that? Argh!), and change -- the evolution of a personality -- is natural. So you might as well wonder if you are the same "you" from five minutes, days, years, or decades ago.

Not to be confused with an Assimilation Plot, in which your identity is subsumed into a Hive Mind. Compare Split Personality Merge, where two personalities become one, and Mental Fusion, where separate minds briefly become one. See also Amnesiac Lover, who doesn't know how to love back after becoming an amnesiac. Grand Theft Me can happen if said identity was stolen. Living in a society where you can't have a real identity is Individuality Is Illegal. See also Quest for Identity. Compare Lost in Character, where an actor becomes lost in a role.

Anime/Manga

 * Carefully analyzed in Magical Girl Lyrical Nanoha, where the entirety of role stems from being considered a mere tool by her "mother" and having the identity of her genuinely loved dead sister, to which her "mother" hates to no end.
 * This is one of the central points in Serial Experiments Lain. Lain is a painfully reclusive girl who barely speaks to anyone, but what about the Lain who spends every night drinking and hooking up at the clubs? Later, when some of The Men in Black are asking her some questions, she asks "Who are you?" They turn the question around, and ask her  She can't answer, because.
 * This is also her source of angst in the final episode, when she wonders who she is after.
 * The point of most Instrumentality plots - as seen on Neon Genesis Evangelion and Yu-Gi-Oh! GX among others - is to relieve humanity of the burden of isolation that comes with individual identities.
 * A major theme of Kara no Kyoukai:. Shiki wakes up after a two year coma and is only able to feel " " - literally nothing, emptiness. She is unable to connect herself to the "her" from her memories, and no longer . Her finding something to continue living for is a major issue for the rest of the series.
 * Also done on a lesser scale with Tohko, who at one point.
 * In Monster, the orphanage Kinderheim 511 existed solely to do this to children of criminals and political undesirables in East Germany. They bit off more than they could chew with Johan, though.
 * A darker take of Ranma's situation could lead to this. Additionally, in an anime-exclusive episode, Ranma banged his head hard after being swatted into the Koi Pond, and was taken over by an alternate personality that thought it truly was a girl, with almost insultingly stereotypical attitudes and tastes, in a situation that was one part this to one part Laser-Guided Amnesia. Fridge Logic on what might be going on with Ranma's real personality while the "girly Ranma" is in control can be Nightmare Fuel if you're a fan of Ranma...
 * Fullmetal Alchemist: As Envy said, the tortured souls that compose his body perished a long time ago in mind and body. This may be true for all other souls that make up the Philospher's Stone.
 * Al is also drawn into a Heroic BSOD by Barry by implying that his memories and body were just crafted by Ed.
 * Happens for real with, who loses his memories and personality, and assumes the role of.
 * Light's in Death Note could be seen as an example of this- when he  Of course, it doesn't last.
 * What he becomes is himself, minus all Kira-related Character Development, but plus the character development of having encountered someone just as smart as himself (L may be smarter, but he handicaps himself with rules so it's hard to tell) and having something interesting going on in his life. Being totally selfish, he wouldn't have become Kira, gambling with his life and self, if he hadn't been bored to the depths of his soul, so there is a distinct difference even from the bright-eyed Light in the early chapters, let alone Kira at his height. Is this still 'him'? Maybe, maybe not. Hence all the questions at the top of the page.
 * A possible outcome of repeating many Groundhog Day Loops in the When They Cry multiverse. At best you come out insane and at worst you come out as a Complete Monster.
 * This is one of the driving forces of Blue Drop: Tenshi no Bokura. The protagonist's male best friend had his brain downloaded by aliens and copied into the body of a female alien, and his real body was cremated. Over the course of the series the copy- and thus the human and masculine identity- slowly fade away, leaving behind the most definitely not human original inhabitant of the body. Worst of all, the human identity doesn't fade away entirely, and by the end, the creature that is left is too human to retain its alien identity, and too alien to retain its human identity.
 * This is an effect of the conditioning given to the cyborgs of Gunslinger Girl, where they are turned into blank slates who can be programmed to perform any function needed and it ensures loyalty to The Handler. That's when it's deliberate, This also happens to Angelica, whose faulty conditioning and implants causes her increasingly forgets things until her death.
 * It also happens when the girls are first turned into cyborgs, as all of them are plucked from near death and it's best to condition over their mental trauma, although Rico still remembers what it's like before the Agency found her and Triela knows that she was found in Amsterdam.
 * In Spirited Away, Yubaba binds people to her service by stealing their names and memories. Even Chihiro who was there for less than a day was already to beginning to forget her real name.
 * In The Secret Agreement, while Kyuusai treats Yuuichi's blood finally awakening as the finding of an identity with the clan (which steals other people's life force in order to live), Yuuichi feels like his identity and all the meaning in his life has just been wrenched away. Particularly since it means his love for Iori is a delusion meant to enable Yuuichi to kill him, Yuuichi doesn't know how to navigate between what he thinks are real feelings and what his uncle says he must do.
 * The driving force behind Kabuto's villainy in Naruto. Kabuto was orphaned and suffered a head injury that robbed him of his memories at a young age, so he doesn't even know his original name or family. The Leaf village employed him as a spy, which meant subsiding his own personality into cover identities on a regular basis. Then he got brainwashed by Sasori and turned into a puppet. He was eventually freed by Orochimaru and found peace of mind acting as his second-in-command, but lost that after Orochimaru was killed. Kabuto eventually decided to focus on attaining power surpassing any other ninja in an attempt to bring meaning to his nameless existence.

Comic Books
"Superman: I tried to decide whether Clark or Superman is more important...and realized that to do away with one would be to kill half of myself--whoever I really am! So even before I got rid of my power problem, I'd decided...meek, mild-mannered Clark Kent will still walk the streets of the city, while up in the sky...the world will still watch and thrill to the sight of--A JOB FOR SUPERMAN!"
 * Superman #296-299 had a storyline where Superman finds himself powerless as Clark Kent and spent most of it sticking to one identity while trying not to fall back on the other. In the end, he had come to a realization:

Fan Works

 * While Knights of the Old Republic fanfic adores this trope, the Brotherhood of Shadow fan-made expansion pack cranks it Up to Eleven with virtually every major character abandoning, obliterating, and adopting new identities. A Twi'lek named Channa Mae was found by Jedi Master Solomon, who nicknamed her "Matilda." When the Mandalorian Wars came, Channa Mae abandoned Solomon and the Jedi, as well as the nickname, to fight for Revan's cause. After the war, she abandoned even the Channa Mae identity to become "Shadow," Revan's assassin/aide/secret apprentice.  Another example is Kobayashi, , then took on a new identity as a scout and smuggler. Solomon also abandons his identity  . The Brotherhood of Shadow itself cements it all - they were an elite Sith order who were critical in repelling the Rakatan invasion of their world, seeing themselves as a single unit, not as individuals..

Film

 * Dark City goes hog-wild with this trope. Every resident in the city (except Dr. Schreber, and even he's not truly spared) is not who they think they are. Every night, The Strangers will go in and mix up a new batch of memories for every person in The City. There is no telling how many years this is going on, and it's highly unlikely that there's any copies of each person's original memories, and thus personality.
 * The Hero's refusal of the serial killer identity becomes a major plot point because
 * The 1996 movie adaptation of Casper expanded Casper's backstory, which involved him slowly losing his memories of his former life when he became a ghost. He does have recollections when he finds his old toy room, but it might just be a matter of time until he forgets who he is again. The idea of ghosts losing the identities of their living selves also becomes a tearjerker when Kat's father turns into a ghost and cannot remember who his own daughter was before he was resurrected in the Lazarus machine.
 * This is the crux for much of the drama in Regarding Henry, starring Harrison Ford. In it, the title character survives a gunshot wound to the head, only for the resulting pinched artery to affect his memory. Cue the rest of the movie depicting him coming to terms with not remembering anything about his life before the shot.
 * This is a major theme of Don't Look Back, as growing inconsistencies between Jeanne's memories and reality cause her to start question who she really is and how many of her memories are actually real.

Literature
"Thomas More: When a man takes an oath, he is holding his own self in his hands. Like water. [Cups hands] And if he opens his fingers then-- he needn't hope to find himself again."
 * Dementors essentially do this to their victims in Harry Potter, and receiving a Dementor's "kiss" is seen as a Fate Worse Than Death.
 * Memory charms are also a means of rewriting a person's memories, and thus creating new identities for them.
 * Intercision in His Dark Materials separates a person from their daemon. At best this means they become incurious and weak-willed, at worst it means they hang around ghoulishly and then die.
 * 1930s pulp hero Doc Savage maintained a secret installation where he used brain surgery and memory modification to 'cure' captured villains' criminal tendencies and turn them into productive members of society -- practices that would be considered torture and brainwashing nowadays.
 * In The Demolished Man,.
 * The Second Trip is about a new person, who was a criminal who had his memory erased and a new personality implanted in him. It is his "second trip" in life.
 * This is the most important theme of Robert Bolt's play A Man for All Seasons. In his introduction to the play, Bolt explains how taking an oath is committing one's whole self to the statement. A man can lose his family, his job, and his wealth, but if he is willing to draw a line in the sand and say "I will not do this thing, under any circumstances", then he probably has a clear sense of who he is.

""All the furniture that made up the way I'd thought and felt about things all my life started coming loose in my head. Nowadays it slides around and breaks into pieces and I have no idea what parts of it are real and what aren't. It hurts, and a lot of the time I don't know who I am anymore.""
 * One of the major characters in The World of Ptavvs is a telepath who seeks to understand aliens by absorbing their memories and worldviews, which become just as "real" to him as his own. Only the fact that he's still in his own body allows him to know which memories are his. Then he absorbs memories from another telepath, an alien who has much more experience with other species than he does, and spends most of the book identifying as and acting like that alien--first thinking he was somehow switched into another body, then being unable to emotionally accept that he's really an inferior human rather than an advanced alien..
 * Memory by Linda Nagata explicitly answers one of the above questions: if you reincarnate, you're not really the you that you once were. You have the same soulmate (of whom there's one and only one even if you can't stand each other), and you're likely to retain some old skills without any idea of how you learned them, but you can change your identity for better or worse, pulling yourself back from the Moral Event Horizon or dropping down into it.
 * In John C. Wright's The Golden Age, Phaethon is suing for his father Helion to be declared dead, because the current Helion was resurrected from a recording an hour before the last version died. Helion repeatedly tries to reconstruct his last hour so he can figure out what he was thinking. What deeply disturbs Helion is not so much the possibility of being declared dead with his son inheriting all as the possibility that he really isn't the real Helion.
 * The Worthing Saga explores this trope in quite some depth as it relates to memory. Every time someone enters Suspended Animation, their memories are completely wiped from their brain, and must be restored from a recording. Such recordings are rather fragile, and if yours breaks, you'd best restart your life from the beginning and relearn what you've forgotten, as trying to live with someone else's memories, knowing that they made choices that your instincts tell you are wrong, tends to cause insanity.
 * The setting also has telepaths, who're subject to a lesser version of this trope. The memories of other people are just as real to them as their own, and if they happen to find a memory they'd rather not have, too bad--it's a part of them forever. The knowledge that they're still themselves tends to ward off insanity, though.
 * One story in the setting, Lifeloop, deals with this trope from an entirely different direction: the relationship between actors and their roles. The main character acts in real-time, unscripted porn films that are filmed over the course of several days, and has learned to fit herself perfectly to her roles. The actor she's matched with for one assignment breaks the fourth wall and confesses that he loves her, not the character she's playing. She goes along, improvising with him, but completely fails to realize that he isn't acting as well.
 * In the X Wing Series, there is a Deep-Cover Agent named Gara Petothel who was trained from an early age to create a personality and a life, fully immerse herself in it, complete objectives including forming and betraying the closest of connections, and shed it without a qualm. To the point where later she can't even remember if her previous identities had friends and interests. At some point the handler who saw her between missions died before she came back into a splinter of Imperial service. There Gara became disgusted with her commanding officer's handling of his crew and arranged for his escape craft to be spotted by New Republic forces, then assumed a new identity and waited to be contacted, getting put into a New Republic fighter squadron. But something was different this time - she was affected by the Power of Trust and genuinely defected. She tried to throw away who she'd been and just be Lara Notsil, pilot, but she couldn't, and eventually her past came crashing in on her.


 * Then things got complicated.
 * Mike Resnick's short story "Me and My Shadow" posits a world akin to that in The Demolished Man, where convicted criminals are "erased" and given benign personalities. The narrator is one of these--except for the part where he still has a little voice in his head that tells him to kill people. And his new personality as an accountant is meticulous enough to make sure that this time, he won't get caught...
 * Happens in the sci-fi novel The Lord Of The World by Russian author Alexander Belyaev. Ludwig Stirner, after realising that he cannot go on with his plans, . Finally, he decides the best way to deal with himself is.
 * In The Ringworld Engineers, Nessus gains leverage over Chmeee by dosing him with (hitherto unknown) Kzinti boosterspice. Because he is now younger and scar-free, he would lose his rather comfortable identity in Kzinti society unless he is provided with evidence to support his story.
 * Chmeee also considers his scars to be part of his personal identity as a warrior, and the loss of them to be almost like losing his memories of the fights where he got them.
 * After spending eighteen years near-catatonic due to losing the ability to feel positive emotions, the protagonist of Greg Egan's short story "Reasons to be Cheerful" undergoes a neurological experiment that gives him the capacity to consciously choose to enjoy or not enjoy things. Cue (w)angst over the fact that all his preferences are artificial, eventually leavened by the conclusion that everyone else' preferences are artificial too, and he's just more aware of it.
 * In John C. Wright's Count To A Trillion, the princess's revelations leave Menelaus wondering who he is.
 * In The Wereling Trilogy, most people who are turned into werewolves become violent and no longer identify with other humans.

Live Action TV

 * Death of personality has replaced capital punishment in Babylon 5. A machine wipes the personality and memory of a murderer and replaces them with a new set, letting them live out a life of willing hard community service with an assumed identity without them ever being the wiser. A telepath is present to perform scans before and after, so as to ascertain that the process has worked, but does not carry it out themself.
 * The Doctor's ability to regenerate is an interesting twist on this: the many incarnations of the Doctor have entirely different looks and personalities, yet they somehow remain fundamentally the same character.
 * Lampshaded heartbreakingly by the Tenth Doctor, who viewed each regeneration as the death of his current self.
 * Also explored in the "Human Nature"/"The Family of Blood" two-parter, where the Doctor's Memory Gambit creates a completely new and separate "John Smith" identity with his own personality and memories, who is terrified at the idea that restoring the Doctor's memories will kill him. Seems like a reasonable reaction to realizing your entire life is a lie and you were invented on a whim by an unstoppable alien mastermind, frankly.
 * In the episode "A Christmas Carol", the antagonist has a MacGuffin device with isomorphic controls which only he can operate, and he is unwilling to help save a crashing space ship. The Doctor meddles with his past, changing his memories and character in the process. When he finally succeeds in changing him to someone willing to help, the controls no longer respond because they no longer recognize him as the same person.
 * Also seen in what happens to victims of Cyber-conversion. The memories remain, but what this form (called "Human.2" by the Cybermen) lacks is emotions and a true understanding of what happened to them. It has been seen that those Cybermen who are made to realize the truth generally blow up, as they cannot live in that form.
 * In a different vein, the TV series Nowhere Man had as its title character a man whose existence has been erased.
 * Joss Whedon has begun to explore the effects of complete mental reprogramming in Dollhouse.
 * It also happened on Angel when he wiped Connor's mind and gave him different memories. And apparently, gave some fairly specific instructions on what he wanted his new personality to be like.
 * An unintentional (... probably) side effect of the Wraith retrovirus in Stargate Atlantis, at least until one of its more notable victims got his hands on it.
 * Done in a rather heavy-handed way on Heroes, in the episode "I Am Sylar".
 * More is sure to come in volume 5 once.
 * Criminal Minds dealt with this in "Tabula Rasa": a serial killer awakens from a three-year coma with total retrograde amnesia. The BAU tried to prove him guilty, but a couple of them raise the point that even if they did prove that the man named Brian Matlof was responsible for the murderers, the Brian Matlof sitting in court could be argued to be a different person. Eventually.
 * In Battlestar Galactica Reimagined a number of characters suffer identity crises of various types. The Eights get the worst of this: Boomer  because she 'doesn't know who she is anymore'. She   have serious identity crises when they   and that

Music
""Please, please tell me what we've learned I know it sounds absurd Please tell me who I am.""
 * Supertramp's "The Logical Song":

Philosophy

 * A related philosophical question is called "The Ship of Theseus": if each plank in the ship is replaced when it starts to rot, and over time one-by-one every single plank is replaced, at what point (if ever) does it stop being the same ship?
 * The Ship of Theseus is also known as George Washington's axe (my grandpa replaced the handle, and my father replaced the head).
 * There's a Kerryman joke to that effect: a Kerryman boasts that he's had the same axe for the past fifty years - with the handle and head replaced, respectively, five and eight times.
 * Specifically, this trope is about the philosophical problem of personal identity. The general notion is that people stay more or less the same throughout their lives, despite changes to their bodies (if these changes do not drastically change the way the body functions). Just what makes several iterations the same person, is central to the debate. The debate itself is notorious for the heavy use of science-fiction examples, such as:
 * Teletransportation: if a teleporter dematerialises you and reconstructs you elsewhere, are the iterations the same person? What if the original is never deconstructed, but a duplicate is made?
 * Brain and/or mind-transplants: are you still the same person when you have a completely different body?
 * Not so much Philosophy but a real life example that I personally believe answers this question somewhat, in "Peopleware" a book about managing programmers a case study was made of "the black team". The black team was had a strong cultural identity that survived after every original member had left. The second generation picked it up from the first, the third picked it up from the second.
 * Hey, this was used in The Fifth Elephant with the hereditary axe. Sometimes the handle needs to be replaced, sometimes the head, but it's still the hereditary axe.
 * And what if the old head, rather than being thrown out entirely, is reforged into a new head for a new axe? Is that also the hereditary axe?
 * Keep in mind this also applies to people. Excluding brain cells, your entire body is completely replaced about once per decade.
 * However that "excluding brain cells" is a pretty big rider, since the brain is often seen as the sole nexus of personhood.
 * No, brains aren't excluded. Old neurons die, new ones are made. It's not just to counteract the wear and tear, but part of forming new memories.
 * In addition, our particles are in constant flux. On the lowest observable levels, we aren't the same from one nanosecond to the next.
 * Even with the cells that stick around for a few years atom that make up the cell wont be same from one month to the next. Your entire body is only a channel for matter, all the atoms in your body wont be within a few months and as creepy as it is a lot of them will probable be in other peoples bodies and vice versa.
 * In The Wonderful Wizard of Oz the Tin Woodman got his body replaced one piece at a time, including his head, when his enchanted axe cut it off. But since it was one piece at a time and not all at once, "he" is still Nick Chopper (his name pre-tinning) rather than some entirely new being.
 * I've read that you, right now, have none of the same cells you had seven years ago, because seven years is the time it takes for the most long-lived cells to die and be replaced, or alternately grow too large and divide. I guess that book - Your Inner Fish - was ignoring brain/nerve cells.
 * A crucial part of Hero's Journey, frequently manifested in the Belly of the Whale.
 * Truth in Television: Lobotomies, this is a surgical procedure where the frontal lobes are removed (or a few vital areas are sliced), essentially destroying the personality of the individual concerned.
 * Phineas Gage
 * It seems to depend. During the period where lobotomies were a popular treatment for troubled teens, a "doctor" developed the non-skull-breaking technique of sticking a thin rod through the eye socket, swerving around the eyeball, and stirring it around in the frontal lobe. There's a picture of said doctor merrily doing this to two patients at once. Results varied wildly. Some people hardly seemed affected at all, aside from being very pissed about it. Brains are complicated things that can form new connections to make up for some damage. That's how despite losing brain cells every year, humans don't peak in intelligence at twenty-five and get stupider from that point on. Brain cells can take up a lot of slack.
 * Lobotomies, in their original form, certainly have a well-deserved reputation for being dangerous and damaging the subject's personality, but modern developments (such as the cingulotomy) are apparently far less so, and can be far more successful in alleviating mental disorders without disrupting an individual's personality. The book Opening Skinner's Box by Lauren Slater devoted a chapter to psychosurgery where she pointed out that cingulotomy surgery tends to be much more effective than conventional psychopharmocological drugs in treating long-lasting mental disorders, but the former is still stigmatized as highly unsafe and invasive, so surgery is rarely carried out. In the US, an individual with severe mental disabilities must demonstrate that a large variety of drugs have had no effect in alleviating their suffering before a cingulotomy will be considered.
 * There's also The Myth of Fingerprints, where fingerprints from say 8 years ago are identified as Alice, but since the entire body regenerates every seven years it's not really the same person.
 * Fingerprints stay the same all your life barring injury, and nerve cells, if none of the others, last a lifetime. Bone cells too can last years. They might just be longer-lasting than the actual bones, which are continuously being broken down for calcium and rebuilt from more calcium.
 * Actually some recent studies have shown that brain & nerve cells do replace themselves, but they do it so slowly that the effect is negligible, which is why it took so long for scientists to notice.
 * That logic was played with by Terry Pratchett in one of the Discworld books. Sgt. Colon, in an attempt to look somewhat more intelligent, makes the 7 years comment. Nobby then raises the tattoo question. Fred's response is that those cells came from other people's tattoos, which might qualify as fridge squick.
 * Cells aren't all like the ones in hair and the outer layers of skin. They don't all get pushed outwards by new cells and slough off. Tattoos are in the skin, not on it. Cells in the skin weaken and are replaced, they come apart and get cannibalized for parts. If that doesn't happen, they undergo mitosis and divide into two cells, genetically "you" but not the same cell as before. Ink stays in that layer. Tattoos do not cause "ink cells" to form. Colon, at least, is excused for ignorance.

Religion

 * According to reincarnation doctrine, deceased souls are brought back to life in another body... but that doesn't mean they come back as a whole person or animal with any memories intact.
 * The Dali Lama is found each time by placing a young child in front of a wide selection of toys; he'll play with the same ones every time. So something is kept in tact (then again, the Lama is said to be able to willingly decide if he reincarnates or not, so there's a belief that he has more control over this than a more less enlightened person).

Tabletop RPG

 * In Dungeons and Dragons, getting bitten by an Ophidian (snake-like creatures commonly found as slaves of the evil serpentine Yuan-ti) results in a not-so-pretty transformation process. After two weeks, the victim fully transforms into another Ophidian, with no memory of its previous existence.
 * Similarly, a Mind Flayer larva devours the brain of a host humanoid, and absorbs the host body as part of its own, in a process called ceremorphosis. The newborn creature has no memory of its host's existence. However, mind flayers scare other mind flayers with stories of the Adversary, a mind flayer who retained its host's personality and, in revenge, dedicated itself to destroying mind flayer society from the inside.
 * Also true of some varieties of slaad (embodiments of Chaotic Neutral), of bodaks (featureless beings similar to but distinct from doppelgangers), and of many varieties of undead. This seems to be associated with magical creatures that are either evil, or so chaotic as to be completely beyond conventional morality.
 * The New World of Darkness uses this often as an example of what happens when your Karma Meter bottoms out.
 * Vampire: The Requiem -- hit Humanity 0 and your Beast takes over, reducing you to a predatory draugr that cares only about feeding.
 * Werewolf: The Forsaken -- hit Harmony 0 and the human half of your spirit decays entirely as some other type of spirit fills the gap, turning you into a zi'ir.
 * Changeling: The Lost -- hit Clarity 0 and you disappear into anything from constant hallucination to utter catatonia
 * Geist: The Sin Eaters -- hit Synergy 0 and your soul departs entirely, leaving your geist to use your body as a flesh puppet to fulfill its strange desires.

Toys

 * In Bionicle, the plan of the Big Bad Makuta Teridax involved trapping the entire Matoran population of Metru Nui into metal spheres, which, over time, deteriorated their physical bodies and wiped their memories clean. The Turaga elders had to reteach everything to them, however one Matoran, Ahkmou, accidentally ended up with Teridax himself, who proceeded to forge a new, evil identity for him.
 * Another example is what happened to the Toa Mata. Due to their malfunctioning canisters, they drifted for such a long time in the ocean that their muscles rotted away (even though the canisters were sealed) and their body parts got jumbled together. When they awoke and put themselves back together, it took some time for their lost identities to reemerge, however only their leader Tahu got his full memories back eventually.

Video Games

 * In Earthbound, when you initially get control of Poo he has an encounter where a spiritual being strips away his body and identity, and even though it's framed as a battle, you can't keep going unless you don't resist.
 * A main theme in Kingdom Hearts: Chain of Memories, where Naminé, was used by Organization XIII to rearrange and implant new memories into Sora's heart to make him a controllable pawn. Also happens to  Roxas, who's memories are wiped by Ansem the Wise and placed in a simulated world with a completely new identity.
 * ...and the villains, who appear not to remember Sora and his gang despite him kicking their asses in the earlier games.
 * This trope is the ultimate fear of Lamia Loveless. When she asked the question "What is left from a soldier, when you take away their mission?", which got rebuked with the answer: "There's still human left!", she slowly starts noticing her identity as a normal soul (despite being Artificial Human). Further interaction and she finally learns to value her own identity, but feared that she would one day turn into a mindless doll, which prompts Kyosuke to promise her that he'd destroy her the moment she ever turns that way... But then, comes the ODE and Duminuss, all who attempted to rob her identity of a new human being and try to turn her into a mindless doll, like the way she was created, and almost succeeded permanently if it wasn't for Axel's interference (and a bit of her willpower).
 * In Metal Gear Solid, after the Cyborg Ninja slices off Revolver Ocelot's hand, he has a Freak-Out upon seeing Solid Snake: He starts to bang his head against the floor while exclaiming that he's losing himself. To fix it, he picks a fight with Solid Snake, egging him on to hit him. It works, because he has been on the receiving end of Solid Snake's punches before, as . Muscle memory trumps brainwashing.
 * Paper Mario: The Thousand-Year Door: Mario gets his identity and body stolen in the middle of a boss-fight by a Duplight-Ghost called "Doopliss". It seems that this even rendered him unable of pronouncing the word "Mario", since Vivian can't understand his answer when she asks him for his name.
 * Nero Chaos in Tsukihime long ago lost his human identity in favor of a collective. The collective is also losing its identify and turning into chaos. Currently, he simply intends to live long enough to figure out exactly what that is.
 * In Phoenix Wright: Ace Attorney - Justice for All, this is part of motivation to murder.
 * Kohan: Immortal Sovereigns does this with its Ceyah faction, who have abandoned Kohan society in search of greater power and adopted new identities; some go so far as to change their appearance by altering their form or donning a mask.
 * The sequel adds new wrinkles to this by adding the Fallen faction - Kohan who have gone so far over the line that even the Ceyah want nothing to do with them; Ceyah who join the Fallen often abandon their Ceyah identities and mutate even farther. The Fallen's leader Abbadon is an extreme example of this; not only has he mutated into a city-smashing monster, but he gains the power to force the Fallen transformation in others, Ceyah or otherwise.
 * Planescape: Torment's entire story is arguably about this trope. Up until the point where the player took over, The Nameless One lost his identity every time he died. Trying to recover just who it is you 'are' through the multitudes of former yous who have existed across time is a cornerstone of the entire game.
 * Cloud Strife is one of the more famous gaming examples of this trope. Going through Heroic BSOD at least twice, unconsciously impersonating his dead best friend, near constant Mind Screw by the game's Big Bad, and then when he really believes that he's just a construct and not the real Cloud. A large portion of the game is about Cloud losing and finding his identity.
 * Persona 2 turned this into even more of Nightmare Fuel with the Joker's curse. Sure, kid! Call in and get any wish you want! Any wish! What they don't tell you is that if you're too weak, Joker drains you of your dreams, hopes and wishes, turning you into a Shadow Self that gradually fades into oblivion as you lose your identity to Joker's crystal skull. And get this - it also works by using a special kinda mask and being exposed to said skull. Kasugayama High just happens to have called for a masquerade dance...
 * Raziel goes through a fair amount of this. Wraith!Raziel (who doesn't remember his mortal life at all, just his vampiric and wraithly existences) meets Sarafan!Raziel and learns that his mortal self is a Sadistic, self righteous Knight Templar douchebag. Vampire!Raziel was still a Knight Templar but working for Kain instead of the Sarafan. Wraith!Raziel is still a Knight Templar at points, but he's the poster boy for Unwitting Pawn and Character Development has left him with higher moral standards than his human or even vampiric self. He even calls his former human self out for his sadism, tells him "I renounce you" and then kills him(self?). Ouch.
 * In Resident Evil 2, Birkin suffers from this after his G-Virus induced transmutation.
 * In the Neverwinter Nights fan module Excrucio Eternum, the elf girl Songbird has literally no sense of self because she has been in a cage her entire life, and has been brainwashed to refer to herself as "it".
 * In the Mass Effect universe this is one of the early signs of Reaper indoctrination. The ability of victims to think clearly and maintain a sense of self degrades and they eventually become little more than slaves of the Reapers, believing them to be gods and the only good thing in the universe. And then come the Dragon's Teeth.
 * Big Daddies in BioShock (series) normally are mind-wiped, but some unfortunately retained their minds.
 * In the Mass Effect universe this is one of the early signs of Reaper indoctrination. The ability of victims to think clearly and maintain a sense of self degrades and they eventually become little more than slaves of the Reapers, believing them to be gods and the only good thing in the universe. And then come the Dragon's Teeth.
 * Big Daddies in BioShock (series) normally are mind-wiped, but some unfortunately retained their minds.

Web Comics

 * In Misfile, Ash is turned into a girl and history is rewritten to reflect that Ash had always been a girl. Even though Ash has a good (apparently better) life, he believes that he can't give in because if he does, it's tantamount to suicide for boy!Ash. Worse, if the misfile is exposed and covered up, he won't have a choice any more. Ash is constantly proving to himself that he's still the Ash he remembers instead of the Ash that the rest of the world remembers.
 * In a recent storyline of The Wotch (which generally tends to gloss over this trope), Ivan wrestles with this after he is transformed via an extremely vindictive punishment for snooping and trespassing by Miranda West, giving us the image, and eventually comes out for the better by reasserting his goals.
 * Depending on how you look at things, Ellen in El Goonish Shive is either Elliot's Opposite Sex Clone, or a magical curse given human form. She has all of Elliot's memories up to the point when she split off from him, and initially believes herself to be Elliot, then snaps and tries to become a villain (with the emphasis on "tries"), then becomes a Death Seeker, and finally
 * This trope is the reason that Justin refuses to allow himself to be permanently transformed into a girl (he knows that a girl being attracted to guys would earn him less ridicule than being a guy attracted to guys). Even if it would make his life easier, he still identifies as a man.
 * In Jack, it's one of the major plot points. The title hero/anti-hero/villain is undergoing eternal punishment for his sins (which, as it later turns out, include wiping out the entire human race) - but his last wish in life, which was also part of the punishment, was not to remember anything. A major motive in the comic is Jack gradually regaining his memories - and the source of many people wondering, is he still the same person when he remembers everything?
 * In Twokinds, this happens to Trace twice: first when his mind is destroyed, and again when he loses his memories. It's theorized that his nice side is real because that's how he was before lost his mind for the first time.
 * In Sinfest Lil Evil foolishly washes himself with the waters of the Lethe and wants to know who he is.
 * Archipelago- When people who knew Blitz before he lost his memory meet him, they all agree that he's a completely different from Anthony, the person they knew.

Web Original

 * Happens in many, many Transformation, Robot, or other such things pictures, stories, comics, and other such things. There's a very good chance that, if transformed into something else, a character will cease to be who they are. Occurs often in the work of Arania, and also in some of the stories of Amhein.
 * http://arania.kamiki.net
 * http://www.process-productions.com/forum/showthread.php?t=16763
 * Also frequently the end result of Age Regression works; after the character is physically age-regressed, they may or may not retain their memories and personality; however even if they do not immediately fall back into childish behaviour patterns, such changes usually happen whether they are preferable or not. This often affects memories as well, such that the process of regression will cause them to forget that they are regressing; it's hard to fight against something that you don't even know is happening to you until it's too late....
 * In Arcana Magi, this happens to Alysia. To the point that she believes her new identity IS her real identity, even though she still has some of her real original memories intact.
 * A common fate of victims in The Slender Man Mythos.

Western Animation

 * In the Teen Titans animated series, Fixit tries to "repair" Cyborg by taking away all that made him human and replacing it with fully mechanical parts and a mechanical brain. Cyborg is justifiably freaked out, because, without his humanity, he'd be just a emotionless machine with his memories. Eventually, it is Cyborg's humanity that causes Fixit to remember what he lost.
 * Spoofed in the SpongeBob SquarePants episode "Missing Identity", where SpongeBob misplaces his name tag and treats it as Serious Business.
 * Xiaolin Showdown - One of the Shen Gong Wu, The Monkey Staff, turns the user into a being with a similar appearance, strength, agility and balance to a monkey. However, if used too long, the user will believe that he or she is an actual monkey, and his or her human memories will be erased until the staff is taken away.
 * Adventure Time has the Ice King, who Was Once a Man, and lost his memory and most of his personality as he lost his humanity to an Artifact of Doom. Its implied he might still be in there somewhere, but buried so deep not even he knows it anymore.

Tropes

 * The Mind Manipulation tropes page would count, since it's about messing with people's loyalties and turning them against their friends and families.