Thoroughly Mistaken Identity

A senile or crazy character has the unshakable conviction that a character is someone else they know -- a specific and actual person, frequently already dead. The most blatant symptom is calling the person by the wrong name, but other inappropriate actions may ensue.

Hilarity Ensues. Or else a horrific depiction of how far gone this person is.

A variation (though somewhat uncommon) is to have the other character not only be alive, but in the same room.

Compare My Name Is Not Durwood. Contrast Napoleon Delusion. Not to be confused with Mistaken Identity.

Anime and Manga

 * Inuyasha: 'My name is NOT Kikyo. It's Kagome. KAH. GOH. MAY.' (Kikyo is Inuyasha's ex-girlfriend, Kagome being her reincarnation.)
 * In Fruits Basket, Tohru's grandfather calls her Kyouko. Kyouko was the name of Tohru's (dead) mother. He is aware of who she is, he just (in his words) "wants to tie them together", as everyone in his life ultimately ends up leaving him.
 * In an early episode of Pokémon, a random woman mistakes Ash for her missing son and calls him "Arnold."
 * In Star Blazers (aka Space Battleship Yamato), Queen Starsha initially mistakes Nova for her own sister Astra, who died in the first episode.
 * In Blazer Drive, this happens to the protagonist when an ill mom mistakes him for her dead son. The protagonist, being an orphan who recently lost his older brother, goes along with it.
 * A Manga (Manhwa?) whose name escapes me featured a girl posing as her dead brother, which was pretty much the only thing keeping her very fragile mom alive.
 * Probably Global Garden. An interesting case in that the girl had latent magical powers that were turning her into a boy to grant her mother's wish without the girl be aware tha she was doing it.
 * Something similar to this happened in Secret Plot Deep, where the main male character's twin sister died in an accident, and his parents were so shaken up about it that they started believing he was his sister. Apparently, they got rid of all the photos of him and forgot he existed. To keep them content, he cross-dressed when at home. This leads to transvestite sex with a girl from school. And a female teacher.
 * In Kongou Banchou, Machine Banchou mistakes little Tsukimi for "Dr. Tsukina", whose orders supersede all others, and she unintentionally alters his personality by giving him suggestions on how to be cooler. This is played for Nightmare Fuel when she realizes the one thing she can't make him do is
 * Also an unusual case of it, as, being a machine, it is frequently pointed out that Machine Banchou identifies people with speech and retina recognition devices instead of, you know, looking at them.
 * In Hayate the Combat Butler, Isumi's mother (Hatsuho) and grandmother (Kokonoe) think they're going to meet the Sanzenin's new butler (Hayate). Kokonoe sees Hatsuho and immediately thinks that Hatsuho is their butler who just happens to look like her daughter. She then realizes who it is and both wonder where the butler went.
 * Hayate was actually visiting, he was standing off to the side during the conversation.

Comic Books

 * The League of Extraordinary Gentlemen has what appears to be an explicit tribute to Only Fools and Horses by not only using this trope, but also reusing the name "Dave".
 * The Queen of Fables, an evil sorceress from a story book believes that Wonder Woman is her arch enemy, Snow White. No matter what evidence is presented to her, she refuses to believe otherwise, and seems completely unaware of the passage of time, as the real Snow White would have died of old age by now.
 * She also mistakes Superman for Prince Charming.
 * Effie in the Ernie/Piranha Club newspaper comic regularly mistakes people for one of her many ex-husbands. (Except Arnold, which she thinks is one of her old dogs.)
 * Enrico the Mole, from the Italian comic strip Lupo Alberto, has addressed the eponymous protagonist as "Beppe" ever since his first appearance. As years went by, Alberto went from his initial bemusement to desperate frustration and eventually to wry resignation. The real "Beppe" (supposedly a friend of Enrico's) has never actually appeared in the strip.

Fan Works

 * In Turnabout Storm it happens to Phoenix twice while in Equestria. First he confuses Sonata with his deceased mentor Mia, something that happens because both have the same voice, and since Sonata looks exactly like Mia would look in pony form. Later on, and more amussingly, he confuses Applejack with Lotta Hart because of the accent, making him completely freak out.

Film

 * In the western Quigley Down Under, Crazy Cora keeps calling Matthew Quigley 'Roy', because, well..... (Roy turns out to be )
 * Which is what made it so significant . The Roy identity also
 * In Batteries Not Included, the elderly and possibly senile Faye persists in addressing one of the other characters by the name of her (dead) son.
 * And in a heartbreaking scene in the end, when said character decides to play along for once and pretends that he is her son,  it causes her to break through her denial and realize the horrible truth...
 * In the final scene of Smoke, Augie poses as a blind old lady's grandson rather than let her spend Christmas alone. Subverted in that she probably realizes that he isn't actually her grandson but goes along with the act rather than admit that she has been abandoned.
 * In Mars Attacks!, senile old Grandma Norris calls both of her grandsons "Thomas". Strangely enough, she does remember their names in some capacity, as she tells Ritchie that "Ritchie" was always her favorite... while still calling him Thomas.
 * In the Sean Penn movie Shanghai Surprise, when Penn's character, Glendon, goes to a fancy restaurant he's mistaken by all and sundry for another character named Phil -- who is never mentioned before or after this scene, nor is Glendon's resemblance. Nonetheless, the fact that Glendon looks like and is mistaken for Phil is a vital plot point without which the movie makes no sense (it's the reason Glendon was picked for the mission, it's how he gets an entree with a lady named China Doll, etc.).

Jokes

 * The whole point of the old Vaudeville joke "I'm not Rappaport".

Literature
""I am very happy, Vandor," she replied, "happier than I ever expected to be in my life." She emphasized the word Vandor, and I thought that I detected a smile lurking deep in her eyes. "Is your happiness so great," I asked, "that it has caused you to forget your vow to kill John Carter?" She returned my bantering smile as she replied. "I do not know anyone by the name of John Carter.""
 * In a Hoka story by Poul Anderson and Gordon R. Dickson, the Hoka Sherlock Holmes persists in calling Alex Jones "Watson" -- the real, which is to say Hoka, Watson is not there, and he can't avoid the pattern.
 * The Hoka stories are a particular variation on this trope. The basic premise of the Hoka stories is that the Hokas (a highly intelligent race that just happen to resemble teddy bears) have trouble distinguishing fact from fiction, so whenever they come across a human novel they end up acting it out and Hilarity Ensues. It's never entirely clear when they do so whether they are conscious of the fact that it's just a re-enactment.
 * Professor Binns in Harry Potter is constantly mistaking everyone for the students of centuries past. It's implied that he's so out of it, he doesn't even realize he died.
 * The Animals of Farthing Wood. After Mole dies, Badger is pretty old and out of it by this time, so when he encounters Mole's son, Mossy, he mistakenly believes that Mossy is his father. Weasel, wanting to be kind to Badger is his last few years, asks Mossy to keep up the charade to spare his feelings.
 * In Dan Abnett's Warhammer 40000 Gaunt's Ghosts novel Straight Silver, some Ghosts find an old woman in the woods, and a deserter that she apparently thinks is her son.
 * In Terry Pratchett's Discworld novel Feet of Clay, Old Mrs Gammage has been going to the same pub for decades. Now deaf, blind and senile, she's completely failed to realise it's become an undead hangout. The "monsters" are too nice to tell her the truth, so when we see her she's cheerfully calling a bogeyman "Charlie", and asking about his plumbing business.
 * In A Hat Full of Sky, old Mr Weavall keeps calling Tiffany "Mary" after his daughter, who died years ago.
 * A particularly old and addled man at a museum confuses Lara Notsil for someone else he once knew. In typical Star Wars fashion, he actually confused her for her mother,.
 * In Chuck Palahniuk's Choke, the protagonist's mother spends most of the book confusing him for someone else, and one of her fellow patients in the nursing home is convinced that he is her brother who molested her as a child.
 * In Vivian van Velde's Now You See It, the main character's senile grandmother keeps calling her by the wrong name. It turns out this is because.
 * In Madeleine L'Engle's A Swiftly Tilting Planet, Mrs. O'Keefe calls Charles Wallace "Chuck." She turns out to be confusing him with her long dead brother.
 * ...who Charles Wallace . Sort of. It's that kind of book.
 * In Edgar Rice Burroughs's "Swords of Mars", he meets, while in disguise, a woman named Zanda, who comes from the city of Zodanga, destroyed because of John Carter's actions. She has sworn Revenge if she ever meets him. She therefore deliberately feigns this trope when she realizes the truth.


 * Caster of Fate/Zero, Gille de Rais, cannot be convinced that Saber isn't Joan of Arc.
 * A woman named Bertha mistook Ephraim Kishon for the guy who made the drawings her dead husband liked so much, in the weekly newspaper he read. Kishon wrote for a daily, non-illustrated newspaper. That is, in the story. It tends to overlap.
 * The Five Find-Outers (well, minus Fatty) once mistook Ernest Goon for Fatty, thinking he was in a clever disguise, and his repeated claims that he didn't know them and wasn't their friend just was a part of the disguise.
 * In Angie Sage's Septimus Heap books, several ghosts always call Jenna Esmeralda. In Physik, she ends up in Esmeralda's time and everyone takes her for her.

Live Action TV

 * Trigger, The Ditz of Only Fools and Horses, insists on calling Rodney "Dave."
 * And it's hilariously deconstructed in a late-run episode when he mentions that the parents are considering naming a baby "Rodney, after Dave."
 * There's an episode of Stargate SG-1 where Merlin repeatedly refers to the team and a few other characters present by the names of people he knew. He calls Mitchell "Percival", Jackson "Galahad", Carter "Guinevere" and Ba'al "Mordred".
 * Raising Hope has Cloris Leachman as Maw Maw, who thinks her grandson Jimmy is her dead husband. Traumatizing Frenching and ass-slapping ensue.
 * An episode of CSI New York drew upon a story from Real Life below. Two girls were in an auto accident. One was killed, while the other survived, albeit badly injured. However, the survivor was later murdered in the hospital.
 * One episode of Lie to Me has Cal Lightman meeting a woman with Alzheimer's Disease who mistakes him for her (dead) husband, and insists that someone murdered her (also dead) sister.

Videogames

 * "Keith, Meg, I'll need you to take over the Wet Noodle when I'm gone!"
 * In The Legend of Zelda: Majora's Mask, Anju's grandmother mistakes Link for her son, Anju's dead father.
 * Then again, the Legend of Zelda timeline(s) are so screwy that goddesses know how many Links there have actually been.
 * Mistaking Link might be a genuine accident, but she definitely uses this to trick her daughter into thinking she's senile as Anju is a terrible cook.
 * Not quite a character, but in Tales of Symphonia, when you meet Raine's and Genis's mother, the poor woman has deluded herself into thinking that she's still pregnant with Genis and carries around a doll that she treats as baby Raine. When the real Raine and Genis appear, she refuses to believe they're who they say they are, and she orders them out of the house.
 * What makes her especially deluded is that given the difference in her two children's ages, Raine would've been ten or eleven when their mother was still pregnant with Genis.
 * The player in Vampire Bloodlines is approached by someone is certain that they recognize you, so certain that they suspect you of being on drugs when you don't recognize them. The only clue that they might actually know who you were is that if you let her phone other friends about you, you lose Masquerade points.
 * To be fair the dialogue options are ambiguous about whether the player did know the person. An alternate interpretation is that the PC only denies knowing the person because they don't wish to associate with their old life now that their vampire form demands a very different lifestyle. The game does make the point that people who associate with vampires often meet misfortune of one kind or another.
 * In Neverwinter Nights, the player is mistaken for the Teller Of Places's dead lover, until the player is able to convince her that she is wrong.
 * In Xenogears, the two main protagonists, Fei and Elly . As such there are several characters (such as Krelian) who are functionally immortal who . Emerelda was . Emerelda refers to Fei as "Kim" and is a legitimate case of this trope in action. Krelian meanwhile.
 * Prototype: believes.
 * Under a different definition of senility, 343 Guilty Spark in the first Halo game doesn't seem to see a difference between Master Chief and his long extinct creators, talking to Master Chief as if they've met before and referring to past conversations they've never had. The matter of who his creators are is one of the many hints across the lore of a connection between the two.
 * It's made explicit by the end of Halo 3, where Guilty Spark comes out and says . This does not, however, stop him from going Ax Crazy when he realizes that in order to save the galaxy from the Flood,.
 * A drunken Oghren from Dragon Age can do this to the player character, mistaking him/her for  Hespith and insisting that he won't let "some kind of moss-biting poetess" march into the Warden's camp.

Web Comics

 * In No Rest for The Wicked, the witch calls the kidnapped children Hansel and Gretel. They explain that they are really Anna and Klaus. Later revelations show that her own children had been Hansel and Gretel and that
 * When Pibgorn takes Dru as "Sylvia", Dru intervenes, seriously.

Western Animation

 * In South Park, Stan's grandfather constantly calls him "Billy".
 * But then again, his grandfather called him Billy.
 * In "Dances With Smurfs" some idiot murdered the 9-year-old morning announcer after he mistook him for the middle-aged man his wife was cheating on him with.
 * All Mr. Magoo cartoons.
 * In The Simpsons episode "The Principal and the Pauper", returning soldier Armin Tamzarian visits Ma Skinner to deliver news of her son, his commander, being taken prisoner by Vietcong. She instead mistakes him for her son and he moves in, eventually becoming a school principal to honor his commander's dream. Judging from her behavior, she actually knows he's not her real son, but puts on the charade anyway. When the real Skinner returns and moves in, she doesn't like him as much.

Real Life

 * When Muhammad Ali visited a nursing home, one man was overjoyed to see "The Champ, the Brown Bomber, Joe Louis!" When one of Ali's handlers started to protest, Ali insisted on going along with it because it made the man so happy.
 * A tragic example in which both identities being dead occurs in the documentary Boy Interrupted: Evan Scott Perry is Driven to Suicide by mental illness, and is laid to rest with his uncle Scott Perry, who was also driven to suicide by mental illness. At the funeral, Scott's mother/Evan's grandmother is wondering why they're having Scott's funeral again.
 * In 2006, Taylor University students Whitney Cerak and Laura Van Ryn were among the victims of a severe automobile accident. Whitney survived; Laura did not. Due to the placement of a purse at the crash site, each girl was identified as the other, and the error was only discovered five weeks later when Whitney had sufficiently recovered from her head trauma.
 * This can happen when Alzheimer's and other forms of dementia get too advanced. It can be very hard on the people in question to continually be mistaken for someone else.