Split Personality Takeover

"Have you ever heard of insect politics? No, neither have I. Insects don't have politics, they are very brutal, no compassion, no compromise. I would like to be the first insect politician. I want to, but I'm afraid, uh... I'm saying...I'm saying I'm an insect who dreamt he was a man and loved it... but now the dream is over, and the insect is awake... I'm saying.... I'll hurt you if you stay. "

- Seth Brundle, desperately pleading his love to leave him before his final transformation into a giant fly in The Fly.

'''WARNING: The presence of a work in the example list is very likely to be a spoiler. Proceed with caution.'''

After months or years of suffering a Split Personality, Demonic Possession, Enemy Within, or Super-Powered Evil Side, the character is cured! ... by having the weaker, "sane" personality lose all control over the body to their inner evil. Like the slow erosion of a mountain, Jekyll has succumbed to Hyde's implacable id-like force, leaving nothing but the shell of who they were.

This isn't just an identity crisis or something that can be wished away with good intentions, at least not easily. This is the permanent and literal death of a person-- or at least a personality.

This is especially common if one personality is more dominant than the other, or the "good" personality is subject to Mind Rape or a Heroic BSOD. Occasionally, a truly strong willed "good" personality can do the takeover-- although it's likelier that they'll choose to "merge" or reintegrate with their evil side into a "whole" personality because Good Is Impotent.

If the takeover is incomplete, expect to see signs that the original is Fighting From the Inside. Antonym to Split Personality Merge. When this is induced by outside brainwashing, it may be Brainwashing for the Greater Good.

Anime
"Even if you stay as Pixy Misa forever, I'll still really love you, Misao!"
 * A variation occurs in Elfen Lied as.
 * Both are okay with that.
 * In Animerica, this occurs to
 * Played straight and very moving and freaky in Trigun, especially the manga: 's short transition from a hugely caring and even oversensitive Cute Shotaro Boy to a Woobie who hides a lot of anguish and anger management issues from his loved ones to  . The anime arguably oversimplifies his transformation and motivations, making his Freudian Excuse quite ludicrous.
 * The manga also suggests that ' original personality may have been pretty ordinary and that he used to have normal human needs, but that it soon got twisted beyond recognition by years of horrifying abuse in a small town plagued by criminality (and pedophiliac homos) in the middle of nowhere-in-Mordor and.
 * It also nearly happens to.
 * Happens to The Count in Gankutsuou, who can almost claim without lying that That Man Is Dead.
 * In Saint Seiya, the Big Bad of the first major plot arc is Saga, Gemini Gold Saint, a saintly (forgive the pun) warrior in Athena's service, whose Split Personality is thoroughly and irredeemably evil. Naturally, it takes over for good, which results in the Sanctuary War, although Saga's good side still shows occasionally (if only to have an Heroic BSOD as his own actions.)
 * This is why Moka never takes off the rosary herself in Rosario + Vampire: the outer Moka would be replaced by the inner Moka forever.
 * Marik and Yami Marik from Yu-Gi-Oh!. The split personality is born when he kills his father. Marik gets his body back.
 * Actually, Yami Marik was born when Marik's father carved his back, the pain was so severe that Marik created a second masochistic personality to cope with the pain. Yami Marik took control to kill his father a year later.
 * In Bleach, this is what Ichigo's inner Hollow intends to do. On a few occasions he manages to briefly seize control of Ichigo's body, but Ichigo has thus far managed to fight him off each time.
 * More eloquent, the spirits that, in time, turn into Hollows, and after the transformation, creatures like Orihime's brother, who fights the hollow within, with little results.
 * Arguably in Umineko no Naku Koro ni. The main villain of the third arc is
 * Inverted with  in Count Cain, who
 * Pretty Sammy quotes this trope to Misao which it encourages her to help her in getting rid of Ramia's evil influence over her.


 * In Psyren when Amamiya is shot
 * Played with in Samurai Deeper Kyo. In the manga version, Demon Eyes Kyo is a legendary killer whose mind has been sealed inside the body of Mibu Kyoshiro, but occasionally rises to the surface. In the anime version, Demon Eyes Kyo is the dark side of Kyo's personality that escaped and became an Enemy Without, then was reabsorbed back into Kyo. In both versions, Kyo eventually assumes full-time control of Kyoshiro's body.
 * Although Naraku already dominates Onigumo, he plans on removing his heart from him since his love for Kikyo prevents him from hurting her.
 * A more classic example comes from Inuyasha himself: whenever in the presence of a powerful demonic aura and/or separated from the Tetsusaiga, his demon blood takes him over and he transforms into his fully demonic form, then proceeds to wantonly murder anyone nearby. It takes an increasingly large amount of effort to bring him back to normal each time.
 * One could argue this is what happened to King Bradley/ in Fullmetal Alchemist.
 * Averted with Ling/, which started off this way but ended up as more a case of Symbiotic Possession.

Comic Books

 * In Frank Miller's The Dark Knight Returns, Harvey Dent has received surgery to repair his face's damaged half, but it has the opposite effect on his mind - Two-Face is now entirely in control.
 * They were right about each half of his face representing one of his personalities... they were just wrong about which side represented which. Oops.
 * Michael Moran does this to himself in Alan Moore's run of Miracleman.
 * There's a Spider-Man arc involving Symbiote knockoffs. Venom, of course, always refers to himself as 'We' (as in, Eddie Brock and his Symbiote), so when one of the symbiotes stops talking in plural, Spidey knows that she's all gone - the Symbiote has taken over her mind.
 * An interesting conclusion of this is that the very thing that makes Venom sound like a raving lunatic is actually an indication of his remaining sanity - or even a psychic crutch necessary for him to retain his identity.
 * Carnage called himself "I" as well, although in that case it was Cletus Kasady, who was already a psychotic killer, who took over the symbiote's mind. The explanation that was recently given is that this was because the symbiote was just a baby when it first bonded with Kasady. Or, Kasady was just SO CRAZY, that he and the symbiote both wanted the same thing.
 * While it wasn't made as big a deal of as the animated version, it used to be that the Goblin Serum gave Norman Osborn a Split Personality, and would periodically forget he had a Super-Powered Evil Side and go back to being an industrialist. Since he came Back From the Dead, it seems to be accepted that he's the Goblin all the time.
 * Though during his time on Thunderbolts and Dark Reign, it seems the split personality explanation is back. Subverted in that Osborn is still an evil jerk, the Goblin is just his darker side.
 * Debatable. This troper always believed that Norman was, if anything, even more evil than the Goblin. Just not in as open, raving, maniacal, blatantly psychotic way.
 * Arguably what caused Brainwave's initial Face Heel Turn after the end of Infinity Inc About fifteen years later, the new personality got possessed by a third, also villainous, personality. Eventually, when the third personality was defeated, it was heavily implied that the third personality ate the second one. In any case, he got better.
 * A horribly tragic case occurred to Dan Turpin during Final Crisis. To be fair it skirts between this and Demonic Possession, but after visiting Bludhaven in search for missing children, Danny starts getting blackouts and finds he can't control himself after a certain point. He then discovers with horror that he is being possessed and/or erased by Darkseid. After he is completely possessed, he is poisoned by Batman, nearly killed by the Black Racer, and finally and utterly destroyed by Superman.
 * The final issue implies, but never outright states, that it was only Darkseid who got destroyed and Turpin was ultimately freed. It's probably a moot point now that DC has reset the universe again.
 * Inverted, to some extent, with the Hulk's son Skaar, where the weaker, more vulnerable personality ('puny' Skaar) has recently managed to escape Skaar's suppression of him in their shared mind.
 * During the Spider-Man storyline The Gauntlet,  worst fears are realized when  ..
 * This was Bloody Mary / Typhoid Mary's (a villainess most often found in Daredevil) entire schtick. She had rather impressive psychic and telekinetic powers, but she also had a horrible case of multiple personality disorder; namely, at least nine of them. Two of them (the aforementioned Bloody/Typhoid Marys) tended to take over more often than not, and there have been at least two instances where one or both have "permanently" taken over only for later events to unlock her original (non-powered) personality once more.
 * In season 8 of Buffy the Vampire Slayer it's shown Oz came very close to going down this road willingly. He had been trying to deal with his werewolf side for a relatively long time, only to learn that whatever he tried was pointless and whatever ground he had gained before was lost. Eventually giving in and simply being done with it all started to look very tempting. It's never explicitly stated why he didn't go through with it, but his words "But I didn't" are coupled with an image of Bayarmaa,.
 * Happened to Ultimate Moon Knight. Doubles as a case of Becoming the Mask, since the personality that took over was created specifically to be more evil and violent.
 * This has happened to Jason Blood from time to time, depending on who's writing the Demon.

Film

 * The ending of the movie Identity.
 * Psycho. "Why, she wouldn't even harm a fly..."
 * The above quote is a hearbreaking example of this trope from the 1986 remake of The Fly. Scientist Seth Brundle slowly transformed into a pathetic and diseased human-fly hybrid after accidentally fusing with said-insect in a teleporting experiment. At first, the deformities were purely physical, as his human flesh warped and decayed into a "cocoon" under which the monster grew. Sadly, he also transformed on a mental level into an instinct based animal, unbound by compassion and morality. The love of Veronica, our heroine, was sadly not enough to stop his predictions from coming true...
 * Averted in the sequel with their son Martin. The murderous rampage against his oppressors is all him. They are bad enough that this isn't a Moral Event Horizon for Martin.
 * Similar to Hide and Seek where
 * Fight Club. Claimed by  to be the evil plan all along.

Literature

 * This happened to Dr. Jekyll at the end of his strange case. Luckily for Victorian England, Jekyll saw this coming and locked himself up before changing completely.
 * He locked himself up because by this time, all of London was out for Hyde's head, after all the atrocities he had commited. Hyde never tries to escape after this point; he just weeps in a corner, because both he and Jekyll can sense the end is near.
 * Happens to some of the Clayborn in David Wingrove's Chung Kuo series.
 * In the Skulduggery Pleasant books, . All of them double as Super-Powered Evil Side.
 * In a rare case of the good side taking over (with a little help), from Gene Wolfe's story "The Death of Doctor Island", the psychotic teenager William, whose brain has been surgically divided between the left and right hemispheres, is deliberately subjected to a devastating trauma which leaves him catatonic. This allows his previously helpless right-brain personality, the calm and placid "Kenneth", to take control of his body.
 * Happens to  in Christine.
 * Happens in Artemis Fowl: The Lost Colony, when
 * And again in The Atlantis Complex. Artemis, having the titular disease, is
 * Happens to one of the bad guys in Shade's Children:
 * In The Lord of the Rings, the character Gollum's darker side of his personality ultimately ends up taking control over his kinder side.
 * Came this close to happening to Tahiri/Riina from the Star Wars: New Jedi Order series. Riina was not "evil", per se- though extremely messed up, she had a Pet the Dog in one of the few times she actually did manage to seize control of their body, and the merge helped Tahiri regain her sanity largely because each compensated for the other's issues (Riina's acceptence of pain and death helped Tahiri get past her emotional fragility following her boyfriend's death, while Tahiri's moral center held back Riina's more violent urges).
 * In The Pilo Family Circus, this happens to every single clown employed by the circus, due to prolonged use of the magical facepaint they wear: it takes around two years of usage for the new personality to completely merge with the clown's brain, but since the facepaint also grants the user superhuman strength, a newly-recruited clown has to wear it just to survive the early months at the circus, and by then, the clown's addicted. Jamie, the novel's protagonist, only just manages to avoid this fate.
 * This happened to a teenager named  at the beginning of Michael Slade's Ghoul. That's especially unfortunate, because
 * The first half of the Dragonlance: The New Adventures series consists of an evil wizard trying to engineer one of these. He implanted the preserved spirit of a powerful evil sorceress in one of his mindwiped servants to try to access her magical knowledge once she took over the servant. Needless to say, the sorceress is rather pissed when she does take over.
 * In Zen and the Art of Motorcycle Maintenance

Live Action TV

 * Played with in Farscape. Thanks to Scorpius' neuro chip, Scorpius' "neural clone" gets stronger and stronger within Crichton over the course of the second season... until taking over completely in the finale. Even after surgery removes the chip itself, the neural clone, "Harvey", never really disappears.
 * Once the chip is removed though Harvey loses any power he had and is basically trapped in John's head forever, with John able to shut him up whenever he wishes. The best Harvey can do to John is be mildly irritating - unless his life is in danger, in which case, Harvey can muster up just enough power to be dangerous.
 * In the Peacekeeper Wars mini-series Harvey finally dies for good when the wormhole knowledge is deleted from John's brain.
 * Basically what happened to Talia in Babylon 5.
 * There was also a rogue telepath in one episode that goes through this.
 * Born vampires from Young Dracula all go through an attempt at this when get their full vampire status. How strong-willed they are seems to determine how much of their original personality is left afterward.
 * Implied to have happened at the end of a Married... with Children episode in which Bud's "cool" personality took over. It had absolutely no visible impact on future episodes (though perhaps that's the joke; Bud's so uncool that even his cool side is uncool).
 * In an episode of Criminal Minds, a young man's murderous and until-then unknown alter-ego permanently takes over his body, in an attempt to protect him.
 * An episode of Stargate SG-1 had Daniel controlled by several different personalities that got in his head.
 * Stargate Atlantis has a similar episode where Rodney and a (female) Marine wind up sharing his body. They each fight over control of the body, until it can't take their fighting anymore: if one of them doesn't give up and willingly disappear, both will die.
 * ...And then they Take a Third Option, of course.
 * United States of Tara: Alice, the "housewife" personality, reveals that she's jockeying to be the emergent personality if Tara ever reassumes therapy. This was followed by Bryce, Tara's alter based on her childhood abuser, who reveals that he wants to "kill" Tara.
 * Jekyll: when Klein & Utterson finally manage to capture Dr. Jackman, they put him into a device that deletes one of the two personalities. Unfortunately for Jackman's wife, Hyde is the surviving personality.
 * This happened repeatedly to Nikki on Heroes when her Super-Powered Evil Side decided to start acting up.
 * In Buffy the Vampire Slayer, this happened to Willow when  died.
 * In The Sarah Connor Chronicles, Cameron experienced a case of this when her processors glitched due to combat damage, and Cameron slipped into an alternate personality mode that thought it was a woman named Allison Young, who was.
 * A positive example occurs on The Twilight Zone. In the episode Nervous Man In A Four Dollar Room, a small-time thug (Joe Mantell) is ordered to kill someone for the first time in his life. His long buried conscience refuses to go along with committing murder and takes over as the dominant personality.
 * In one episode of Tales from the Crypt a lonely man's only companion is his own split personality. When the man starts dating a therapist, said split personality is afraid that she will destroy him and tries to goad the man into killing her. When the guy refuses, his other half decides to "kill" him and take over his life. In the end, the more assertive personality has cowed his former boss and is on the fast track to becoming an executive and is married to the therapist.

Other

 * Bionicle: In one of the alternate universe Takanuva stumbles through, the alternate Makuta Teridax absorbs Matoro, who failed in his mission to save Mata Nui in this universe. When Makuta absorb other beings, they normally absorb their bodies and minds, but Matoro fights back, killing himself and Teridax, becoming the hero he was destined to be.
 * The video for Foo Fighters' "Breakout" has a meek Dave Grohl becoming the rock star Dave Grohl after losing both his medication and his shit (inspired by Me, Myself and Irene, on which the song was included).

Tabletop Games

 * The Harrowed from Deadlands are constantly in danger of this, since they owe their very existence to the demons possessing them. Except Stone.

Video Games

 * In Twisted Metal: Head-On,
 * The bad ending of Soul Nomad and The World Eaters involve this, with Gig using your greed to destroy the main character's soul and taking over his/her body.
 * Both the good and the evil ending of The Suffering: Ties That Bind
 * The bad ending of Manhunt 2- achieved by killing people as gruesomely as you can - has.
 * Near the end of Planescape: Torment you get trapped in a place where you encounter three of your previous "incarnations". One wants to take you over so and another simply wants to destroy you. If you manage to forcibly take over the other two or get them to merge with you, you will gain their memories (and a ton of XP). If you fail, you have to destroy them and their memories are lost forever. The third takes no convincing to get him to merge with you and is more than happy to.
 * Vampire: The Masquerade Bloodlines has a scene where, after being led along by the two, you finally confront . Depending on the dialogue you choose, either
 * Done very strangely in the Warcraft series; Arthas was a paladin who is corrupted by the Lich King, becomes his champion, then later merges with him, but then Arthas takes over the Lich King, an entity of godlike mental power. A dark lord taken over by another dark lord  when they became one dark lord.
 * One of the main plot points of Riku's story in Kingdom Hearts: Chain of Memories and its remake is that Riku is fighting off the last of Ansem's darkness within his Heart. Several times he almost falls to it, and once he actually does, however how it happens depends on the version. In the original after completely dominating Lexaeus in their fight, the latter blows himself up in an attempt to drag the latter down into the Darkness, however in the nick of time he is able to resist. In the remake however, after a stalemate battle Riku lunges at Lexaeus to finish him off, only to be backhanded into the ceiling and passing out. Unconscious Riku's body is possessed by Ansem who then kills Lexaeus in one hit before Mickey appears and frees Riku.
 * Fubuki Shiro, who is taken over by Atsuya, his inner mind's high ego little brother.
 * A positive example can be found in Deadly Premonition, where
 * In Mortal Kombat 9 a positive example appears in Ermac's Arcade Ladder ending. eventually becomes dominant in Ermac and becomes Edenia's protector again.
 * Super Robot Wars Alpha 3: Subverted
 * In The Elder Scrolls verse, the Daedric Prince of Order was cursed by the other Princes with this.
 * This is the major twist in the freeware Visual Novel Ori Ochi Onoe.

Western Animation
"Green Goblin to Harry Osborn - "Your whining simp of a father doesn't exist anymore. I am the ultimate evolution of Norman Osborn!""
 * Norman Osborn undergoes this in Spider-Man: The Animated Series.


 * He undergoes this before being sent into another dimension.
 * In an Aladdin episode, when a botched experiment leads to Mozenrath and Aladdin sharing the same body, Mozenrath tries to do this. He isn't successful.
 * X-Men: Evolution, episode Sins of the Son. Charles Xavier discovers he has a son in Scotland, David Haller, and goes to meet him, only for two other boys to enter the fray as well. These three boys (David, Ian, and the evil Lucas) are all parts of the same being. Xavier tries to help expunge Lucas,

Web Original

 * A curious example in Red vs. Blue: Reconstruction - when an AI is implanted in a character, the effect is described as being "of the same mind", where the two entities share thoughts. Though the host is usually able to maintain his or her identity (even if free will is lost), Agent Maine (better known as the Meta) degenerated into a mindless husk after playing host to 7 different AIs at once and stayed that way even when the AIs were removed. Of particular note is the fact that all 7 AIs were Literal Split Personalities of another AI, the Alpha.
 * Whateley Universe example: Sara Waite is really a Great Old One who is supposed to evolve into The Kellith, a being who will wipe the earth of humanity and re-populate it with her spawn. She ends up having a fight to the death with The Kellith in a Journey to the Center of the Mind.

Real Life

 * An episode of the dramatized court-case anthology series The Judge dealt with a female dissociative identity disorder patient who, in the episode's surprise twist, turned out to be the victim of her psychiatrist, who was having an affair with her Femme Fatale persona and plotting to destroy her original personality so the two of them could be together. While the script might've involved some dramatic exaggeration, there are real-life cases of secondary personalities in DID cases plotting to kill their primary selves, without recognizing that if they're successful, they'll die too.