Among psychologists and mental health professionals, Dissociative Identity Disorder is probably one of the most controversial 'disorders' ever. In real life, Dissociative Identity Disorder (or DID) is a condition believed to be most common among survivors of sexual and/or physical abuse that occurs in their childhood/teenage years. There is some controversy as to whether or not it even exists. This is because virtually all cases seem to occur only in the U.S, the U.K, and Canada- in other words, where movies that have protagonists with DID are popular (Sybil, The Faces Of Eve, Fight Club, etc). In point of fact, Sybil, the Trope Codifier herself,may not have had DID at all. Diagnoses of DID skyrocketed following the release of Sybil from maybe one or two diagnosed cases a year to several thousand. This suggests to many psychologists that it's less an actual disorder and more of a fad, since otherwise there'd be a better distribution of diagnoses in other countries and it wouldn't follow movie trends like this. The actual diagnosis rate of DID is maybe <1 in 1000 to 1 in 10,000. It's exceptionally rare. It's normal to act differently around other groups of people (we're obviously going to act differently around friends, family or employers) - blacking out for extended periods of time and 'losing control', with no recollection of it, is not.
As it is understood to modern psychology, the condition is thought to sometimes result when a child/teen copes with abuse by convincing themselves that it's happening to someone else; as such, the trigger is generally some experience the child/teen is trying to dissociate themselves from, by means of creating an "alter" who gets put in charge. Note that without recieving psychological counseling the symptoms will carry over into adulthood. The individual has no control (at least initially) over when the personalities "switch," and may not initially remember what happens to them while they are switched. To put all that in Tropese: you go to your Happy Place while some poor Red Shirt has to deal with the Trauma Conga Line or Humiliation Conga - so stereotypically the personality who has to deal with it is not a nice person...
But that's not entertaining, so television does it differently, and in several different ways. Two (or more) personalities may be sharing memory or not sharing memory or have access to each others' memory as external to their own in symmetric or asymmetric fashion, they can switch at will or involuntary and be in clear war or some form of pact. It even may be the very same personality (i.e. having the very same mind, memory and desires), but changing 'behavior mode' between several clearly distinctive states.
Characters with a split personality are surprisingly common in fiction, but most of them don't quite match the textbook definition of DID. In older media, it will often be called "schizophrenia" even by psychologist characters.. (The word schizophrenia literally means "split mind," because a main symptom is scattered, unconnected thoughts. It's more like being on a really bad drug trip, and can actually be induced via crystal meth overdose (caused by too many stimulants in the brain at once) - but please, Don't Try This at Home.
See also Double Consciousness, Identity Amnesia, Jekyll and Hyde, Superpowered Evil Side, Split Personality Merge, Split Personality Makeover, Split Personality Takeover and Talking To Themself. If the split personality is the antagonist, it's the Enemy Within. Shapeshifting is sometimes involved. If the personalities are flipping back and forth, Flip Personality often ensues.
Compare Trauma Induced Amnesia.
If the two personalities are aware of each other, expect a Gollum Made Me Do It situation to develop. Resolving it may require the weaker of the two to say "Im Not Afraid Of You!" If the Split Personality gets its own body, it becomes either a Literal Split Personality or an Enemy Without (if said personality is antagonistic or evil).
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Nyu/Lucy in Elfen Lied. One's has the mental capacities of a small child, the other's an insanely powerful killer out to take out a significant portion of humanity.
It turns out that Kaede is actually a fairly neutral identity, who's just been listening to a third Omnicidal Maniac personality (the 'real' Lucy) that wants to end all life.
It seems that most, if not all of the diclonii have a "neutral" personality and their inner voice that tells them to exterminate humans. Especially apparent in Nana's case, where when pushed, will become just as violent as any of the others.
One one side we have Misao Amano a Shrinking Violet schoolgirl who transforms (unknowningly and involuntarily) into Pixy Misa, the evil magical girl. however, this trope is subverted when it was revealed in episode 19 that her alter ego was in fact just the repressed aspects of her personality so the audience was lead to believe that the Pixy Misa persona was due to brainwashing when in fact Misa and Misao are one and the same.
The Prince of Tennis' got a good one. Seigaku's Takashi "Taka" Kawamura is a kind hearted guy whose father owns a sushi restaurant, but whenever he grabs a racket, his "burning" mode is turned on and becomes Seigaku's top power player.
Yamamoto Jun from Special A turns from a relatively shy guy to a cassanova whenever he is kissed by a girl. Later on it seems to be when a certain girl just looks at him.
Zetsu has two well-differenced halves. His right side is black and speaks in a deep voice, while his left side is white and talks in a lighter voice. Both halves can talk with each other, and sometimes argue! Later, we see that he can even split his personalities (and body) into two different halves. The black half is ultimately revealed to have been infused with the "will" of Madara prior to his death, while the white half is the original Zetsu.
Jugo's powers cause the split personality but activate independently, and as such, the change between the two has nothing to do with whether or not he uses his powers.
Lady Une of Gundam Wing developed split personalities out of her love for her boss Treize, one a cold-hearted, calculating Colonel Badass, the other a kind, soft-spoken peace advocate. She has a few moments of near breakdown before being shot roughly halfway through the series and remaining comatose until the final arc. The coma apparently gives her time to resolve her issues, and when she wakes up she has Iron Une's military and strategic skills and Saint Une's compassion and desire for peace. Her glasses act as a trigger. Once she puts them on, you're guaranteed to see her order somebody's death.
The "Other Momoka" as well as Private Tamama. Both appear sweet and harmless at first, but they hide an extremely jealous and possessive side that occasionally comes out when a perceived "rival" for the object of their affection appears.
Momoka's mother turns out to be the same way, except she prefers to let her aggressive side be the default; this is the reason she doesn't live with her loved ones.
Parodied in one episode in which a cute detective channels her late father whenever she puts on his hat.
At the end of the series, Il Palazzo shows another kind of split personality, becoming possessed by his own desire to conquer. This was a definite case of a Super Powered Evil Side, along with elements of demonic possession. In the manga, which had more time for these things, the split personality is more of a subversion, the only real differences being the fashion sense and preferred targets - neither are evil or good, and both are slightly insane.
It's still a bit unclear how Lord Il Palazzo's personalities work in the manga. Sometimes it seems that it's only a case of varying amnesia, vaguely remembering and forgetting things from his past, which shape his motives. But one consistent difference has been that sometimes he is fond of Excel and tries to get her to remember something (maybe), while other times he wants her gone. It's also unclear which personality, his caring or uncaring one, is his true personality.
Yami Yugi in Yu-Gi-Oh! is initially presented as one of these, before it is revealed that he is actually the spirit of an ancient Egyptian pharaoh. The same goes for Yami Bakura, but not Yami Marik, who is a more traditional split personality caused by childhood trauma. Ironically, Yugi's GXsuccessor is a true example.
Mahoraba's Aoba Kozue has five personalities, switching to one at random whenever she's shocked or surprised. Her eye colors change for each personality, and each personality prefers to wear her hair differently. She switches back to normal by going unconscious. While each personality is pretty distinct from the rest, they all have several distinct traits they share, particularly a liking for her crush and a major thing for umeboshi.
Shinobu Sensui in Yu Yu Hakusho was a lawful yet pure and innocent young man before encountering the Black Book Club, rich men who tortured demons for fun. He couldn't bring himself to kill humans (as opposed to demons), and so developed another personality to do the dirty work. Over the years, he developed six alternate personalities, switching between them depending on the situation (I.e: he used the Magnificent Bastard "Minoru" to recruit his followers and pull strings, then when Yusuke managed to hit him he switched to the Ax Crazy "Kazuya"). Each one has a different level of power; the original one, Shinobu, is the most powerful of them all... and is still an innocent, as he let the others do the dirty work.
In the manga Othello, the shy main character Yaya switches to her alter ego, bold and assertive Nana, when she sees her reflection.
In Cardcaptor Sakura, Yukito Tsukishiro turns out to be the "disguise" of Yue, Kero's counterpart. Yue changes into Yukito on purpose, but Yukito has no idea Yue exists and cannot remember anything that happens to Yue. He doesn't know that his comically large appetite is because he's actually eating for two (the other being a powerful magic-user). He later comes to realize what goes on when Touya gives his powers to Yue so neither he nor Yukito would disappear.
SZS managed to pull the inverse of this: one personality split among many girls, thanks to Fuura being Dead All Along and her organs going to the girls in her class.
In Sukisho, both Sora and Sunao developed split personalities, Yoru and Ran respectively, due to experiences they were subjected to as children. The catch: the split personalities Yoru and Ran have a romantic relationship...unlike Sora and Sunao. Every now and then the split personalities will take over and some, or, depending on the degree of the situation, extreme awkwardness follows
Allelujah Haptism has a rather psychotic other half that he calls Hallelujah.
Marie Parfacy has one named Soma Pieres. Soma "goes to sleep" definitely in the second season and [[Marie returns to be]] the one in control.
Air Gear: The perky, happy Akito has another personality, the violent and curse-spewing Agito, who was created after his older brother locked him in a cage and forced him into fighting against other AT users. Who's in charge can usually be indicated by his Eyepatch of Power (Agito's is over the left eye, and Akito's is on the right). The manga, however, went even further and introduced a third personality named Lind, who seems to be more mature and worldly than the two of them.
MPD Psycho really drives this trope to utter extremes. Some of the multiple personalities even appear in other physical bodies, and this even when their original physical body has died. Which might make this manga a slight twist. (It's amazing what the average corporation can do while trying to bring a Not Quite Dead rock musician back to life.)
Tyki Mikk of D Gray Man has commented how having a light side and a dark side makes life more fun. He can be a perfectly ordinary, personable man, but is also a tremendous sadist and has killed at least five Exorcists, including one of the Generals. Most of the other Noah have similar Split Personalities, albeit somewhat less extreme.
Yumie Takagi, berserker soldier of the Iscariot Organization in Hellsing. The (not canon for the series) Cross Fire stories in the first three manga volumes involve her being brought out for various assassinations, to the dismay of her other personality, a thoroughly sweet nun named Yumiko.
The webcomic And Shine Heaven Now takes it one step further, where it's revealed that aside from Yumie, Yumiko has nine more personalities that were being suppressed by Iscariot. She suffered a temporary Heroic BSOD when Heinkel released them as the personalities sorted themselves out. In a big Shocking Swerve though, Yumiko was never the original personality. She was just led to believe she was because she's the easiest to control.
Jamie Hemeros in Zoids: New Century/Zero develops a cocky ace pilot alter-ego named Wild Eagle who takes control during battles every now and then. Although popular opinion seems to suggest that this happens when Jamie breaks the sound barrier in his Zoid, Wild Eagle actually seems to appear only when Jamie gets overly stressed out in battle.
In season 2 of Princess Tutu, Mytho starts to complain of "another me" being inside of him, an evil personality that quickly begins to take over more and more. Later, it's revealed that it's actually the result of one of his heart shards being tainted with Raven's blood.
InuYasha has Suikotsu of the Band of Seven, who has three personalities: a kind and caring doctor who has no awareness of the other two (and is the original one), an ultra-violent killing machine who knows of the other two and despises his gentler personality, and an "in-between" personality who is aware of the others and serves the Band of Seven while remaining calmer and more rational than his bloodlusting counterpart.
Motoko in Change 123 has three split personalities named Hibiki, Fujiko, and Mikiri - collectively known as HiFuMi (1, 2, 3) - that materialize whenever she's in danger. These split personalities come from her Training from Hell under three different adoptive fathers. Changes in hairstyle, muscle structure and cup size come with itnote Also, in the colored promotional panels their eyes and hair usually have different colors. (See "Color-Coded For Your Convenience" item in this manga's "Characters" sub-page!) , along with martial arts styles — each personality, other than Motoko, are martial arts masters in a single specific field.
A 5th personality emerges at one point called Zero. Zero represents all of Motoko and HiFuMi's negative emotions, and is very unstable — Oh, and she has all the other personalities martial arts expertise, at the same time, and is super strong, to boot. Later it's discovered that Zero is actually Motoko's first split personality, her "Mr. Hyde", created when she forcibly locked away her anger (because she superstitiously believes that her anger killed her mother).
Suzuho in Macademi Wasshoi is usually quiet and meek, communicating only through sketchbook messages. When she removes her ribbon, her other side comes out, which is the exact opposite in personality. Violent, talkative, and, for some reason, blue-haired.
Paranoia Agent has a woman whose split personality (who is far more promiscuous and thrill-seeking) leaves messages for her on her answering machine; threating ones. Frightening stuff.
This is actually a moment where MPD is depicted accurately. There have been recorded cases of personalities threatening other personalities. (Even going as far as causing bodily damage)
The title character of Paprika, who is the dream avatar of Dr. Atsuko Chiba. Paprika is everything that Chiba isn't and secretly wants to be. And it gets better: Paprika has characteristics of both Chiba and Tokita, hinting at the former's affections for the latter.
The Big Bad in Part 5 of Jojos Bizarre Adventure has two personalities. There's Doppio, a borderline autistic, childlike man, and Diavolo, a cunning, violent and paranoid mafia boss. His hair color, eyes, and size change drastically and his Stand power changes form as well. Doppio communicates with Diavolo by holding random objects to his face like a phone (after hearing schizophrenic ringing).
Usopp from One Piece may be developing this. When it was first introduced, "Sogeking" was an assumed name and Paper-Thin Disguise Usopp used (the reasons are complicated). Usopp acted rather differently while in his Sogeking disguise, even managing to score his first realBig Damn Heroes moment before reverting back to his old, cowardly self after circumstances changed and he was able to remove the mask. During a later fight (as Usopp), he is actually depicted mentally arguing with Sogeking. Later still:
Usopp: * Running away from Perona and Bearsy* "Somebody, save me! Save me!"
Sogeking: * Tackling and purifying a goddamn zombie bear* "Save me, Sogeking!"
Averted in Kara no Kyoukai: Tohko correctly identifies that what Shiki used to have before her coma can't be dissociative identity disorder, given it's complexity.
Shiki: "There's nothing funny about having a dual personality." Tohko: "No, no. You know, you two don't have anything as pleasing to look at as dissociative identity disorder. Existing simultaneously, each having their own unique will, and on top of that your actions are coordinated. That sort of complex personality shouldn't be called a "dissociated identity," but rather a "united independent personality."
Nobara Ibaragi in Gakuen Alice has some sort of split personality - one personality adores and wants to protect Mikan, and the other does whatever her evil 'teacher' tells her to do.
Hohenheim from Fullmetal Alchemist is revealed to suffer a sui generis, mindblowingly over the top case of this. Long story short: he is a human Philosopher's Stone, these are made out of many people's souls, do the math. He has devoted most of his life to isolate, communicate with and befriend each of these 536329 different people "living" within him.
Johan is indeed a real person, but Inspector Lunge (or Runge) is convinced that he is an alternate personality of Dr. Tenma.
Wolfgang Grimmer, meanwhile, occasionally blacks out when physically threatened. When he recovers, everyone who threatened him is dead. He refers to the personality that takes over as "the Magnificent Steiner", after a show he watched as a child (where the title character is the superhero persona of an unknowing boy).
In King Of Thorn, the English translation says Alice has schizophrenia, but it later becomes clear that it's actually DID - being abused by her family caused her to develop an alternate personality called Laloo, who would take the abuse for her. After she became infected with Medusa, Laloo manifested as an Enemy Without.
This becomes the premise of Nanaka 6/17, once the title character's original personality re-emerges in early story, after a Laser-Guided Amnesia period in which she reversed to her 6-years old mindset. And in the manga only, aside from the 6-year old personality, Nanaka develops in the second half of the story a second split personality, which names itself "Hiro".
Lain, the main character of Serial Experiments Lain, seems to have several as the series progresses: shy, schoolgirl Lain, a very famous "Lain of the Wired" who's arrogant and powerful, and a manipulative and sadistic Lain. It turns out that there are an endless number of possible Lains, as each and every person's perception of Lain, and each concept of Lain that arises via Memetic Mutation in the Wired, becomes another one of her facets. Eventually, though, they undergo a Split Personality Merge into a kind-hearted, but extremely powerful, Lain.
In the Hentai manga series Bondage Fairies, the fourth manga - Extreme - introduces Urushira, an old flame of Pamila's. By day, she's a sweet and caring doctor. At night, her other personality - a nymphomanic Psycho Lesbian who is oh-so-very Yandere over Pamila, takes over. And when she wakes up the next morning, she doesn't remember a thing that her dark side did last night.
As of Chapter 284, Asuna seems to have developed this as a result of having her Laser-Guided Amnesia forcibly undone: one is her "true" personality from before Ala Rubra rescued her from her life as a living weapon, and the other, currently dominant, is the Asuna we've come to know and love.
Luna, too. Ironically, her other personality is also Asuna.
Black Lagoon's favorite Creepy Twins, Hansel and Gretel, crank their typical Nightmare Fuel on this trope and share split personalities with each other. They could decide themselves who wanted to be Hansel and who wanted to be Gretel at the time, to the point that there is Wild Mass Guessing as to which one was actually which at any given point during their story arc. There are even some that believe that both were the same gender, as to which that is left up to debate.
Count Cain reveals in its Wham Episode that the Riff that all the characters knew was actually a fake personality, created by the Delilah Organization. The real Riffael was an awful, cruel man, and when he's reawakened he immediately betrays the protagonists.note Many readers suspect that this was partly The Tower being duped like he was over the zombie thing, and that while 'the original' wasn't the greatest guy he was a more normal human being than either of his halves. Thus, Riff cutting his wrists in guilt over surviving his family, even though he doesn't remember that he set the fire, is an enaction of Riffael Raffit's self-hatred that he was too proud to express and The Tower doesn't even feel anymore.
Hatsuharu, the ox of the zodiac, who turns into 'Black Haru'. Black Haru usually comes out when he's angry and while Haru is usually easy to get along with, no one can handle his other side.
There's a milder version in Kagura, the boar, who is sweet and mostly caring but becomes possessive and quite occasionally violent when Kyo is around. Either tsundere to the extreme or possibly a bit yandere.
Both could be considered oddly realistic takes, as well. Neither are shown to be aware of the changes, except from what others tell them (Kagura is even confused about why Kyo looked so beaten after one incident), and we've seen just what caused them to develop and triggers the changes. Haru's "Black Haru" personality developed as a result of verbal abuse and his overwhelming resentment of Yuki, and he only changes when angry (harder toachieve than it sounds). Kagura, on the other hand, switches when something threatens to expose that she's trying to love Kyo to get over her past guilt.
Gemini Saga, from Saint Seiya. The specifics are never made terribly clear (i.e we don't know exactly how it developed and came to exist), but it takes hold of him and causes him to murder and impersonate the Pope (not, not that Pope) for a number of years and generally act like a self-entitled asshole.
Irabu-sensei from Kuuchu Buranko has a total of three personalities: Stuffed Animal one, who acts silly and childish, Child one, who acts more serious and snarky, and Adult one, who is something inbetween but leans closer to Animal one.
Angel Sanctuary: An interesting subversion with Alexiel and Setsuna. Setsuna is (currently) the dominant persona while Alexiel steps occasionally as his Superpowered Badass Side whenever he's in over his head. Although each has a completely differentcharacter, Setsuna still occasionally echoes some of Alexiel's words and personality, proving that they really are the same person deep down.
What about mild-mannered Negishi from Detroit Metal City, whose alternate personality Johannes Krauser II is the badass and feared leater of a Death Metal band?
In Kotoura-san, Detective Tsukino has one, due to being bullied as a child. Her evil personality was in charge or revenge and was also the perp of the physical assaults on school girls in episode 10. With the help ofHaruka, the good side is able to eliminate the evil one and she is even ready to turn herself in to pay for "her" crimes, which is refused by her superior, whom she has an apparently close friendship with.
Two Face alternates between the just Harvey Dent and the maniacal Two-Face. Despite being the most well known example, he is also an abnormal one, because as Two-Face, both of his personas, good and evil, are "on" at the same time (Usually. Two-Face is a huge case of Depending on the Writer). Coincidentally, his symptoms sometimes imply actual Schizophrenia, which doesn't exactly help clear the confusion people have about the two conditions.
A few comics have suggested that The Joker has multiple personality disorder, switching from a harmless prankster to serious threat and everything inbetween.
Even Batman himself has been accused of this. By day, he's Bruce Wayne. Put on the costume, and he's a completely different person. It's even been argued that the Batman persona is his "true" personality, and Bruce Wayne is the mask he hides behind. Grant Morrison's run on Batman revealed that Batman, who prepares foreverything, deliberately cultivated a back-up personality should the Bruce Wayne/Batman persona be incapacitated.
Arnold Wesker is a mild-mannered ventriloquist, and is utterly convinced that his psychopathic mobster alter ego, Scarface, manifests through his ventriloquist's dummy, rather than his own brain. Scarface often agrees with this, and the split personality's dependance on the puppet is so strong that the personality doesn't manifest outright when the puppet is missing or destroyed, although poor Arnold then feels a compulsion to replace it.
Some stories imply that Wesker is correct, and the doll really is possessed by an evil spirit or spirits (in his last appearance, Wesker dies and the doll is burned...and gets up and walks before collapsing). And a couple suggest that Wesker is just acting and the doll is really just a ruse to convince everyone he is crazy. Much like The Joker is sometimes accused of being, but given some of the stuff Scarface has put him through note At one point Wesker replaced Scarface with a sock puppet; Scarface returned and they shot each other, leaving Wesker with bullet ridden hands, Wesker would arguably be even worse.
When Wesker replaces the Scarface dummy with a different puppet, the alternate personality is often different, and usually milder mannered.
Dr. Bruce Banner is a different person when transformed into the Hulk. The comics take it to extremes, with different versions of the Hulk with different personalities: in addition to the traditional "Savage Hulk", there also developed a sneaky, amoral version called Joe Fixit (who was grey, like in the Hulk's first appearance). Eventually, the personalities were integrated into the "Merged Hulk", but this was retconned to be just another personality, the Professor (who had Banner's brainpower, Fixit's cunning, and most of Savage Hulk's strength).
Two other personalities in Bruce's lineup are the Devil Hulk, a reptilian creature that lacks any sense of guilt, and the Green Scar, who combines Fixit's cunning with the Savage's strength, and over time develops to become possibly the strongest Hulk incarnation of all.
The Hulk's son Skaar also has a split personality; "normal" Skaar is a Conan-style barbarian, while "puny" Skaar is an adolescent boy who hates his other self for his savage deeds.
Some have theorized that the Hulk is - and always has been - an embodiment of pent-up rage and aggression that Banner had felt all his life prior to the accident, mostly stemming from the abuse he and his mother suffered at the hands of his father. Who Bruce killed by accident, but later admitted it might have not been an accident. In short, Banner and the Hulk may be more alike than Banner is willing to admit.
Grant Morrison's run on Doom Patrol featured, among other characters, Kay Challis, also known as Crazy Jane, who had no less than 64 separate personalities, each with its own name and function, and after a "gene-bomb" was detonated during an alien invasion of Earth, each with its own superhuman ability.
Triplicate Girl/Triad from the Legion Of Super-Heroes tends to show signs of this trope when she splits apart. The version of her in the Post-ZeroHour reboot was explicitly written as having three distinct personalities when split — which was considered a mental illness on her homeworld, although her grandmother insisted it was natural, and suppressing the different aspects was what was unhealthy. The current version takes this a little far; her entire civilisation consists of triplicates of the same person. The one/three who are members of the Legion, however, have had so many different experiences from the others that the rest won't let them rejoin.
The DC Comics character Etrigan the Demon was bonded to a man named Jason Blood as punishment for being tempted by Morgaine Le Fay into betraying Camelot. Jason switches places and lets Etrigan take over when there's superheroing to be done. (He's a prime example of Cursed with Awesome.)
Actually, Blood and Etrigan are truly two separate beings, so this Trope is technically inaccurate.
The DCU also has had two different Rose and Thorn characters over the years, one whose Thorn persona was a villain, and a later one whose Thorn is a hero.
There is a Star Wars comic, where after a Jedi kills a love in a fit of jealousy she develops a dissociative disorder. One personality is a crazed killer, murdering women that remind her of the one her love was cheating on her with, while the normal personality obsessively "chases" this killer.
Jeanne-Marie Beaubier, aka Aurora of the Marvel Universe's Alpha Flight, had at least two separate personalities when first introduced: the demure and timid "Jeanne-Marie" and the forthright and fun-loving "Aurora". Flashbacks in an early issue of Alpha Flight revealed that the "Aurora" personality split off from "Jeanne-Marie" after she was severely beaten by the nuns who were raising her. Originally, only "Aurora" had superpowers (not surprisingly, since the nuns had beaten Jeanne-Marie for telling them she could fly — she could, but they assumed she was lying), and if too much stress caused her to revert to the "Jeanne-Marie" personality in a crisis, it could cause serious problems. In her more recent appearances, she's shown signs of having a third, unnamed, personality, whose main characteristic is being psychopathically violent.
X-Men: Similar to Crazy Jane, Professor X's son Legion originally possessed three personalities with a distinct psychic power (one was telekinetic, one was telepathic, one was pyrokinetic). This was later expanded to an unnamed number of personalities - possibly thousands - ALL with a unique power. Unfortunately, when these personalities were successfully merged, the new, improved Legion decided the best thing to do was to travel back in time to kill Magneto (he missed, killing his own father and unintentionally spawning the Age Of Apocalypse timeline).
Mary Walker, a supervillainess most commonly associated with Daredevil, has three distinct personalities. The "Mary" personality is a timid, quiet, pacifist; her "Typhoid Mary" persona is adventurous, lustful and violent; her "Bloody Mary" personality is sadistic, brutal, and hates all men. Typhoid was so different than Mary, that even Daredevil was, at first, unable to tell the two apart, even with his enhanced senses. (It seemed that the change even affected her body odor somehow.)
Insane robot and villain Ultron. Every model has a new, different personality, culminating in one version which contained every previous personality constantly vying for supremacy, making him eight unstable megalomaniacs in one.
Ultron gets it honest, apparently, as his/her creator and 'father' figure, Dr. Henry Pym, underwent a period of insanity where he not only believed himself to be a different person, but claimed to have actually killed Pym. While this was eventually resolved, he's still not the most stable of people, to the point that when he was Skrull-replaced, they went through multiple agents specifically because each one that imitated him eventually developed his mental problems and had to be eliminated to keep the cover from being blown.
The Sentry and Void. The Sentry is 'The Golden Guardian of Good', blonde haired, handsome and heroic, his powers being strongest during the day. A fangirl's dream version of Legolas, wielding more power than Silver Age Superman with added psychological problems, and a broader power set to boot, which is officially unlimited, facing down beings like Galactus and Green Scar (the latter when extremely agoraphobic) and winning or drawing. The Void is a pure evil, manipulative Eldritch Abomination in semi human form, strongest at night or in the Negative Zone, and is often described as akin to the Angel of Death. Both wield planet busting power, and are immortal effectively by choice. Whenever the Void turns up or The Sentry looks like he's about to lose it, it's a Mass Oh Crap moment for the entire Marvel Universe.
Moonstone, a psychiatrist by trade, describes the Sentry/Void dichotomy as a 'split personality conflict playing itself out through comic book archetypes'. She also adds that it would be pathetic if the two weren't each able to destroy the planet.
Shasti from Adam Warren's version of the Dirty Pair is an Artificial Human deliberately engineered with four personalities for different tasks.
Copycat from DV8, whose five personalities are each represented by different fonts and word balloons. Ivana actually points out the Hollywood Psych at work, saying that Gem's condition doesn't resemble any case of Dissociative Identity Disorder she's ever read about. She theorizes it has something to do with her Gen-Factor mutating an existing psychological disorder.
There's one story by German comic writer Walter Moers with a "schizophrenic" guy who says that he "counts for two" because of his two personalities, of which he is aware, and who switch pretty fast. One of them is pretty boring and essentially just says things like "me too". Yes, it's neither correct nor PC.
Peter Milligan's reboot of Shade, the Changing Man has this in droves, with Shade, his heart, his suit, his skin, his alter-ego Hades, and others all forming, taking control, leaving, and rejoining the hero.
Moon Knight started off with the gimmick of having multiple secret identities. Depending on the Writer, this became a disassociative personality disorder, with Marc Spector, Jake Lockley, Steven Grant and Moon Knight all being distinct personae. He also sometimes believes himself to be in communication with the Egyptian god who gave him his powers, but that might be another personality. Currently, he's got one "main" personality, but is recieving advice from hallucinations of Captain America, Wolverine and Spider Man.
GI Joe originally had a "Psychological Profile" for Zartan that describes him as an "Extreme paranoid schizophrenic. Grows into various multiple personalities to such an extent that the original personality becomes buried and forgotten." Mental health groups complained, however, and Zartan's psychological profile had been dropped in later reprints of his general profile.
One of Zartan's Dreadnoks is Road Pig, real name Donald DeLuca. This isn't mentioned in his toy profiles, but in the comics he's depicted as having two distinct personalities: thuggish half-wit Road Pig and cruel sophisticate Donald. They're aware of each other, and though there's not much they agree on, they both love wanton destruction and Zartan's sister Zarana.
ThisAUKingdom Hearts fanfic portrays Sora, Roxas, and Naminé as three sides of the same coin, with Sora as the "original". The summary splits them even further, which is confusing. So far the story revolves around Naminé's relationship with her Love Interest, Marluxia, and him trying to get used to Sora and Roxas.
North Korea OC characters in Axis Powers Hetalia fandom tend to be either this or the Evil Twin of the canonical South Korea. This trope often comes into play in fics dealing with civil war.
Pinkie Pie had several created by her refusal to accept certain parts of her. Pinkie Pie (the "normal" personality), Pinkamena (the personality she created to take any sad or unpleasent things she doesn't want to feel), Diane (the part of her who loves her biological parents and her home), and Pinky (her childhood memories). The truama Discord put her through resulted in the birth of Angry Pie (an Ax Crazy psychopath representing her repressed anger) that tried to eat her other personalities. Pinkie performs a Split Personality Merge becoming one still wacky but far more sane Pinkie Pie..
Her Dark World self, Angry Pie brute forced her mind back together, resulting in her mental self looking like a poorly sewn together ragdoll. After stealing Twilight's Element of Magic, it begins to awaken her old memories, Twilight then nearly kills her while almost going Nightmare, and then Twilight (once she's talked down and gets back to her old self) uses a reverse version of the Memory Spell (showing Pinkie Twilight's memories instead of her own) to destroy Discord's taint. The combination of all this causes her mind to break apart again into Motherly Pie (her motherly side who wants to take Discord's Deal with the Devil to resurrect her adopted foals), Friendly Pie (the part of her who still loves her friends and wants to protect them), Guilty Pie (the part of her who is guilt-ridden by what she's done for the last thousand years), and Lost Pinkie (her memories of the Lost Age that was erased in a Cosmic Retcon). Twilight goes into her mind and has to convince the personalities to merge back together, resulting in a sane Pinkie Pie who's able to redeem herself.
Fluttershy and Fluttercruel: Fluttercruel is her own individual being with her own soul, they're just Sharing a Body. However, Fluttershy actually has a split personality in the form of Flutterage, born from her repressed anger. In the end she also does a Split Personality Merge and becomes whole.
The Immortal Game: After Twilight Sparkle is freed from the Sliver of Darkness, the trauma of everything that's happened causes her mind to split in two — the Actual Pacifist Sparkle (the dominant mind) and the more brutish Twilight (who talks to her, but has no control over their body). This lasts until her torture at Titan's hooves causes her personalities to fuse back together.
Several Harry Potter fics involve Harry suffering from non-canonical more extreme Dursley abuse and developing split personalities as a result, sometimes with later personalities emerging due to the various traumatic events at Hogwarts. In one story it was Voldemort who had the split personality and after a psychiatrist/Death Eater got his psycho personality to go into "hibernation" he became Harry's mentor and supported him in his dreams of becoming an Auror, while in a similar story the Voldemort persona was the result of an experiment in creating split personalities that was backed by Dumbledore.
It is eventually revealed in the Reading Rainbowverse that Octavia's sister is actually her split personality.
Gollum and Sméagol ("Stinker" and "Slinker") from Peter Jackson's The Lord of the Rings live-action movies. The two personalities frequently carry on conversations, to the point that they're practically two minds consciously coexisting simultaneously in the same head. This split-personality theme is less pronounced in the earlier animated movies and the original books, but still present. See entry under Gollum Made Me Do It.
In the moviePrimal Fear, the shy and gentle Aaron, on trial for killing the archbishop, is revealed to have a split personality named Roy who is much more outspoken and aggressive and did in fact kill the clergyman. At the end, we also find out that Aaron doesn't actually have a split personality; the more disturbing truth is that Roy created Aaron and has been hiding behind the fake personality for years.
In Adaptation, Donald Kaufman writes a script titled The Three, in which the serial killer, the cop chasing him, and the victim the cop falls in love with are all the same person. His brother Charlie points out how idiotic and filled withFridge Logic the film is.
In the movie Peacock, the painfully shy John (Cillian Murphy) has more confidant personality named Emma who makes him breakfast and lays out his clothes every day, like a wife would—which is precisely what everyone thinks she is when she is accidentally discovered. The personalities are aware of one another, but they have no memory of the other's experiences. John gets increasingly panicked as Emma begins to 'control' him more, and Emma eventually 'murders' John by staging his death and presenting as Emma only.
Surprisingly averted with Two-Face in The Dark Knight. Several other diagnoses can surely be made. For one, he still likes to make simple moral decisions based on a coin flip, and acts... should we say, chaotically. He uses uses the coin when deciding the fates of the people he holds responsible for everything that happened to him in the last day or so. He's on a revenge spree, using the coin to illustrate the arbritariness of it all.
Black Swan clearly is meant to make the viewer think this is going on, but it ultimately leaves it ambiguous as to whether Nina has a split personality or not; the case could be made either way.
In Psycho Beach Party you learn very early on that Chicklet has at least two other personalities.
Carter in Raising Cain has several, including the amoral Cain and his "fall guy" Josh.
Hide and Seek David tries figure out his daughters imaginary friend Charlie and who he is. The Reveal was David is Charlie, and Charlie was the one who murdered his wife.
One of the protagonists in the Russian comedy Gun with a Silencer "becomes" a woman between midnight and noon. One hilarious scene involves "her" being examined by a gynecologist, who takes one look at the plumbing, drinks a shot of vodka, and says "she's healthy".
Happens to some of the Clayborn in David Wingrove's Chung Kuo series when under severe pressure.
Mark Meadows, AKA "Captain Trips," of the Wild Cards series. Normally a smiling, weirdly dressed and rather ineffectual hippy (albeit one with great skills in biochemistry), in time of need his various powders and potions are capable of making him an ace of badass proportions .... or rather, several aces, depending on which one he takes. All of them have a different mind and personality, and most of them think the good Captain is a wimp or worse, and do everything they can to keep from reverting when the chemical wears off.
In The Lord of the Rings and related materials, it is suggested that Gollum's personality developed from Sméagol talking to the Ring ("my precious") which he eventually identified as part of himself, as well as his desire to place the blame for the murder of his friend Déagol onto someone else.
Gollum's split personality never appeared in the first edition of The Hobbit: it only shows up first in the rewrite, when Bilbo hears them discussing after realizing that Bilbo had the Ring all along. At the time of writing the first edition, the Ring wasn't evil yet in Tolkien's mind, and so had no reason to poison Sméagol's mind.
Subverted in Blindsight: one of the characters is a linguist with three surgically-induced alter personalities (known collectively as the Gang of Four). Some time is taken up in discussion of twentieth-century attitudes towards MPD, which are largely dismissed as barbaric and irrational. The Gang are a relatively realistic depiction of D.I.D cases where all of the personalities know of the others' existence and cooperate.
This is apparently not that uncommon on the Discworld. Perdita is explained as having come about specifically because Agnes took a part of herself—her desire to not be a nice girl with a good personality—and gave it a name. Her senior witches muse to themselves that giving something a name gives it life, too. Rincewind's conscience and Sam Vimes's inner rage are also sometimes depicted as semi-sentient, especially in Night Watch, where Vimes refers to it as "The Beast". In Thud!, we find Vimes also has an "inner watchman", who ends up kicking a powerful vengeance spirit out of Vimes' mind.
Mightily Oates also suffers from this, dividing into a skeptic part and a devout part. At one point he considered having himself exorcized. And, like Agnes/Perdita, he is resistant to vampiric mind control, because they can control only one mind per brain.
Thud!! also features Pointer and Pickles, the owners of a rock collector's shop, who turn out to be the split personalities of the same woman.
Lord Mark Vorkosigan, from Lois McMaster Bujold'sVorkosigan Saga, developed four extra personalities to resist torture: Gorge, Grunt, Howl and Killer. While he learns to control them, they explicitly do not go away. Fortunately they are all fixated of protecting/aiding Mark to the best of their abilities from the getgo and like his girlfriend.
Mark's brother/progenitor Miles hovers upon the verge of this trope when is undercover identity of Admiral Naismith threatens to become a fully separate persona. Mark also laments that at least Mile's alter ego is the sort of person you can dress up and take out to a party if the need arises compared to his far more primal alters.
Ted Dekker's thriller novel Thr3e (as well as The Movie of the Book): The killer who's been chasing the protagonist is actually a split personality of the protagonist. But wait! Isn't the title "three"? That's right! It turns out his childhood friend who's been helping him solve the mystery is also one of his split personalities.
Sidney Sheldon's novel Tell Me Your Dreams is about a woman who fears she is being stalked, and her two co-workers who become concerned about her. It is eventually revealed that all three are the same person; the main character developed two separate personalities because she could not handle the trauma of childhood sexual abuse.
In Stephen King's The Dark Tower series introduces two characters in the second book: Odetta Holmes, a fairly well-to-do black woman who lost her legs and is generally surviving the 1960's as best she can; and Detta Walker, who is dangerous, brutal, and very bitter. The two personalities are almost completely unaware of each other, at least until the plot comes knocking. At the book's climax, the two personalities integrate into Susannah Dean, who possesses the good sense of the former, and the tenacity and will of the latter. Odetta/Dedda is irritatingly referred to by all characters and narration as "schizophrenic."
In Amelia Atwater-Rhodes' Persistence of Memory, Erin suffers from DID with the complication that her alter comes from psychic residue from a vampire attack on her pregnant mother. While the alter that manifests is just the psychic remnant, the basis for Erin's alter, Shevaun, is a very real and very dangerous vampire.
X-Wing Series: "Runt" from Wraith Squadron] manages to skirt the reality issue by being, well, an alien - he has a number of highly specialized minds, such as the Pilot and the Student; this is noted to be natural and healthy for his species, and learning to switch quickly between personalities is helpful for him. Lara Notsil/Gara Petothel/Kirney Slane, though she might appear to fit the trope and once dreamed of her different personae arguing, is really a spy who started Becoming the Mask and soon had a genuine desire to defect, as well as some unstable identity issues. No split personality.
Matt Ruff's novel Set This House In Order is about Andrew Gage, the "public face" of a multiple personality. And that's just the beginning.
The Dragonlords are born with two souls/identities: one human and one dragon. This overlaps into Sharing a Body in that the two personalities are fully aware of each other and converse at times. The main character, Linden, has trouble controlling the anger issues of his dragon side, Rathan. His mate's infant-like dragon side refuses to acknowledge her.
This is the big twist of Fight Club. About 2/3 through the book, the reader and the narrator find out that Tyler is the Narrator.
Severian in The Book Of The New Sun who is both the original torturer Severian and also Chatelaine Thecla after eating the Albazo (and Thecla.)
Janis Cordelia Plumtree in Earthquake Weather by Tim Powers, whose condition is complicated by the fact that one of her personalities is actually the spirit of her dead father.
Ellen Hopkins' Identical has a more realistic case of this. Near the end it is revealed that Kaeleigh has DID and Raeanne is her other personality. The real Raeanne died in a car accident during the twins' childhood
In Artemis Fowl, Artemis gets one because of his Atlantis Complex.
Done in a fairly realistic way in Matt Ruff's Set This House In Order with two characters who both have DID. Both suffered severe abuse as children, but one has been aware of this problem for a long time, and all the personalities work together and see a psychiatrist. The other character is younger and less aware of what is going on, and is afraid because she keeps having periods of memory loss. Both characters eventually work towards the goals of overcoming abuse, getting treatment, and choosing between full integration and trying to function by having all personalities cooperate with each other.
In the two part Fear Street story Fear Hall, it turns out that Hope Mathis' three friends, Jasmine, Angel, and Eden, as well her homicidal boyfriend Darryl are actually split personalities, created due to her mother's abusive treatment towards her.
Rand al'Thor and Lews Therin fit this trope as well as anything else. It's difficult to determine if it's caused by madness from use of the One Power or being a reincarnation of the original and the voice is actually a real being. In any way Rand certainly thinks he's suffering from madness. At the end of the 12th book, they pull a Split Personality Merge, after which it's explicitly stated that they 'aren't two men and never were' - that is, Rand is most definitely the reincarnation of Lews Therin, and he also most definitely had some access to snippets of Lews Therin's memories and knowledge as a result, but the 'voice' of Lews Therin that Rand conversed with for six books was merely a symptom of his deteriorating mental state.
The series also includes a couple of weird borderline examples with the recurring villains Padan Fain and Slayer. Fain merged imperfectly with the soul of the Evil Chancellor Mordeth, and though he thinks of himself as one personality he has two distinct sets of mannerisms which he'll switch between randomly and apparently unwittingly, and sometimes he'll forget which of the two names he's currently using. Slayer is actually two distinct men named Luc and Isam who share a body; they were combined into one by the Dark One but retain discrete identities to the point that when which personality is dominant changes, the body also changes to reflect it.
In the New Jedi Order series, teen Jedi Tahiri has this after a Shaper's attempt to transform her into a Force-using Yuuzhan Vong fails- Tahiri retains her original personality, but the Vong personality can't be excised and remains in her subconscious. Ultimately, Riina (Tahiri's Vong half) tries to pull a Split Personality Takeover, but when she and human Tahiri prove too connected for this to work out, a Split Personality Merge happens instead. The resulting person calls herself Tahiri, but has the memories and experiences of both.
In one Animorphs novel, The Separation, Rachel's personality goes so far as to be split into two physically different people—one timid, gentle, and pacifistic; the other ruthless, violent, and obsessive—when she gets cut in half while in starfish morph. Because of starfishes' regenerative powers, she "grows back" a whole extra person.
Joe Ledger has a committee in his head: the Civilian, who keeps him sane but is unable to deal with his day job; the Warrior, who just wants to hurt someone; and the Cop, who combines the best of both, being honorable but still a fighter.
In Michael Flynn's Up Jim River, Donovan. His multiple personalities were induced deliberately, but the manner was bungled—also, perhaps, deliberately.
Iliana Ghemor in the Star Trek: Deep Space Nine Relaunch. She was implanted with the memories and personality of Kira Nerys as part of an undercover operation. Now, she has both her original memories and Kira's, and considers herself the rightful inheritor to the real Kira's life. Because Kira set the bomb which killed Iliana's betrothed during the Occupation of Bajor, she also has a split perspective on his death — as both the guilty party and a victim.
In The Heroesof Olympus, the conflict between the Roman and Greek camps causes some serious issues for the gods, since there are equal calls for their Roman and Greek sides. This causes the sides to battle for dominance, the consequences of which vary in severity depending on how different the Roman and Greek aspects are. Gods like Aphrodite/Venus or Nemesis walk off scot-free, since the ideas of love and revenge are the same in Greece and Rome. Hercules/Heracles gets headaches, but otherwise it isn't too bad. Athena/Minerva is reduced to a scatter-brained wreck and Dionysus/Bacchus can't remember Percy and gets a blinding headache when Percy calls him Dionysus instead of Bacchus. The issue is apparently grave enough for them to be rendered incapable of dealing with other problems until the issue is resolved.
Most Aristoi cultivate multiple "daimones" to help them multitask.
Live Action TV
In the Night Visions episode Switch, the protagonist, Sydney, has multiple personalities.
Dollhouse has two: Alpha and Echo. However, Echo only gets it the last two episodes, and they're both a literal case of many personalities.
Niki Sanders on Heroes has "Jessica", the personality of her dead sister, as an amoral alter ego with super-strength. Some people just can't handle having superpowers and the stress causes a dissociative break, making this one a quite literal Superpowered Evil Side.
When "Jessica" kills their father in early S1, it's made clear that he was abusive to the point of killing Nikki's sister Jessica, after whom the alter ego is named. Only the "Jessica" alter remembers, which resembles real theories of DID fairly well. In S2, a third, party girl personality, who apparently began as a mere alias, emerges.
A patient in Private Practice was alleged to have this condition she was diagnosed at the age of seven and partially raised by her older sister she hasn't had a resurgence in ten years they came back with the stress of her sister moving away. She was actually faking so that they won't move.
While this is a staple trope of daytime soap operas, the soap One Life to Live took this to an extreme. Not only did established character Victoria Lord Buchanan develop a number of personalities (the most notorious of which was streetwalker Niki Smith, a full contrast to Viki's upper-crust manner), her daughter Jessica later developed her own split (tough girl Tess), as a result of a retcon where a young Jessica follows Niki to a bar and gets raped by a guy and this was caught on tape.. Apparently, in the OLTL universe, split personality is a genetic disorder. In addition, Viki's brother, Todd Manning, at one point was also thought to suffer from DID, with 5 separate personalities: the original Todd, Tommy, a little boy who was the abused Todd as a small child, Rodd, an Italian-accented charmer and Peter, a representation of Todd's abusive step-father, and a strict female personality that served as the Gatekeeper. At the end of the storyline, Todd admitted he'd been faking all of the personalities, but as he left town (the actor was leaving the show) a last scene showed Todd and all of his personalities on the plane.
The United States Of Tara: One character has four alternate personalities: a sex-and-drugs addict 15-year-old called T; a disturbing Stepford Smiler housewife named Alice; and a male, rowdy, alcohol- and brawls-loving motorist called Buck; along with the mysterious Gimme, who was unknown even to Tara and serves as a kind of "pure id/protector" alter, who comes out whenever Tara gets too close to discovering something which might traumatise her.
Seasons Two and Three introduce three more personalities: Shoshana Schoenbaum, an alter based on a therapist Tara creates after reading said therapist's book, Chicken, who is essentially Tara when she was five years old, and Bryce Crane, an alter based on Tara's half-brother who is believed to have sexually molested Tara when she was a child and is the reason why she has DID in the first place. Bryce then proceeds to apparently kill all of the other alters, although the last episode reveals that Buck, T and Alice are still 'alive'.
In the third season of Homicide: Life on the Street, a serial killer turns out to have multiple personalities, including a seven-year-old girl. One detective tricks this personality into burning herself, so another personality sues the precinct. However, it is implied that this may all be a ruse on the killer's part.
Shawn and Gus run into a character with three personalities on Psych. Two are male, one is a female, and one is the killer, who is (understandably) a little ticked off that the female personality is scheming to get a sex change. When Gus points out how rare the condition is, it is hand-waved by Shawn pointing out it only has to happen once to be true.
On the British soap opera Holly Oaks, troubled emo kid Newt has an alternate personality called "Eli", who trashes the Deans' house and encourages him to run away from his foster home. In recent episodes he now plans to find and kill the real Eli (a friend from his days in the social care system) in the hope of banishing the "Eli" personality.
On Ally McBeal, one client was the original personality, who wanted treatment to get rid of the alter-ego, who hired another firm to protect its existence. The court found in favour of the original personality, which the treatment then unexpectedly eliminated. This is wrong, as the treatment for DID is to integrate the personalities together.
Baywatch. A woman develops a split personality when her twin sister dies. Her two personalities both become obsessed with Mitch Buchannon. One personality takes over and tries to drown him. The real topper is the woman is played by Carrie-Anne Moss years before The Matrix.
Nip/Tuck one of the episodes is Montana/Sassy/Justice one wants her ankles fixed and another one wants her breasts gone because she is 5, this is the same person.
Law & Order: Special Victims Unit has had a multiple personality woman (Cynthia Nixon) killing her abusive dad She gets not guilty by reason of insanity, she was faking it
In The Sarah Connor Chronicles episode "Allison from Palmdale," Cameron suffers a glitch due to combat damage she took earlier in the series. As a result, she takes on a completely different identity and personality, that of a girl named Allison Young, a future resistance fighter whom her body was modeled after and then subsequently killed. By the end of the episode, she recovers, though not without supplying the stuff of many an unpleasant dream in the process.
In one episode of Stargate SG-1, Carter likens being host to a Tok'ra symbiote to having schizophrenia. They meant DID. Apparently, they later did their research, and as though to pay penance for their error, made an episode where Daniel Jackson actually got schizophrenia from an Applied Phlebotinum that was intended to kill Goa'uld.
Since DID patients generally aren't aware of their other personalities, but some schizophrenia manifests as hearing voices in your head, maybe they did mean schizophrenia. The Tok'ra host and symbiote are conscious at the same time regardless of who is controlling the body, and communicate with each other mentally.
Criminal Minds used this twice: once in second season, when Reid was kidnapped by a man with three personalities, one of whom tortured him, one of whom drugged him, and the last of whom played Russian roulette, and once in fourth season, when the rapes and murders of young men in Florida over spring break turn out to be the work of a woman named Amanda in the body of a guy named Adam. In the first case, all of the personalities were aware of each other, although it's not clear that they knew they inhabited the same body. In the second, only the secondary personality is aware of the condition, which leads to a Split Personality Takeover.
The Doctor Who audio Omega has a sort-of case of this: Omega, half of whose personality is under the delusion that he's the Doctor and that Omega isn't inhabiting the same body as he is. However, it's clearly not DID and has rather more sci-fi causes.
An episode of Lie to Me has Cal take a client with this disorder. Cal has to figure out which of her several personalities witnessed a murder. Although the character is initially referred to as having a split personality, Foster corrects the speaker and instead says that she has DID, which is the term used for the rest of the episode. Foster also notes that DID is very rare, assuming it exists at all.
An episode of Forever Knight features a woman with two personalities, one of whom is a normal mortal and the other a vampire.
1960's Batman series. Professor William Omaha McElroy, an Egyptologist at Yale University, would become the villain King Tut every time he was hit on the head and return to normal when he was hit on the head again. He would be the only series villain never sent to jail, via the insanity defense.
Prof. Mc Elroy also knew about his Tut self (despite not recalling what he did under ) also tried to prevent King Tut's emergence via wearing a special hat supposed to soften blows to the head. Obviously, it didn't work.
This is the premise for the Russian comedy series Zaitsev+1. The protagonist, Sasha Zaitsev (sometimes Latinicized as Zaicev) is a typical college nerd who is in love with Nastya, the prettiest girl in his class, although she doesn't know it and stays with her cheating Jerk Jock boyfriend. Whenever Zaitsev gets hit in the head, is blinded by a bright light, or is deafened by a loud noise, he turns into Fyodor, his wild, rude, and cynical alter ego who likes big women. While Fyodor is actually played by a different actor, only the audience perceives him as a different person. Everyone else just notices that Zaitsev is suddenly acting very differently. Fyodor likes to sleep around, especially with another girl named Nastya, which becomes a problem for Zaitsev, who can't really explain his problem to others without sounding insane.
The Season Nine finale of Law & Order: Criminal Intent, "Three In One", has a character who legitimately has three personalities as opposed to faking. The following spoiler will tell you whether any of them did anything illegal. Yes. He ended up that way because of severe childhood abuse, which his female abuser told him was "discipline". When he grew up, hearing any adult woman talk about the importance of disciplining a child made him remember his own "discipline", which made him angry and afraid and brought the "protector" personality to the surface. The protector would then attack and kill the woman, whom he believed was advocating and participating in the abuse of children.
Highlander had an immortal with a split personality. The good side, Michael Moore (no, not THAT one), was a good friend of Duncan's. But the evil side, Quentin Barnes, slowly overpowered Moore and Duncan had to keep his promise to stop Barnes. In an earlier time, the evil side actually killed the good side's girlfriend.
Murdoch Mysteries features a suspect in a murder that suffers from this in the episode "Me, Myself, and Murdoch".
Played for laughs in an episode of Night Court, where a defendant's DID wasn't revealed to the main characters until near the end. One personality was prudish, the other was slutty. The episode's running gag was for her more "open" side luring Dan into some private (and always off-camera) location for some hanky-panky, only for her prudish side to re-emerge just as things were apparently getting good.
In Grimm there was a kid who was unaware that he was Löwen, his Löwen side developed an separate personality of its own, and started killing people who were smarter that him, which was its way of protecting him.
Sanctuary has Adam Worth, a genius with a split personality. It's a bit confusing, since both are, apparently, named Adam. The split started after his daughter got sick and died. He blames the Five for this.
The main hook of Do No Harm: The title character is an ethical doctor who switches to a malevolent second personality at 8:25 pm each night. After keeping this personality sedated with drugs for years, one day he finds that his body has become immune to them...unleashing the other personalty, now bent on destroying his life.
Renard, oh lord, Renard. Some of his artists pseudonyms, in rough alphabetical order, are: Adraen, Azrael, Bloomin' Nutters, D-Mode-D, Detergent, Emoticon, Furries in a Blender, Hecate, Jackal Queenston, Jaql, Kitcaliber, Kitsune, Klippa, Lollipop, Mayhem, MGD-Crew, MGD Assault Force, Mr. R, Neko, Plusfuchs, Renard, Perdique Darron, Sigma, and Sonitus Vir, as well as some others.
On Maeror Tri's Multiple Personality Disorder, each track corresponds to the function/role each personality tends to assume, based on now-outdated psychological theories about the condition:
1. The Administrator
2. The Anaesthetizer
3. The Revenger
4. The Protector
SHeDAISY's song "Lucky 4 You" uses multiple personalities in an almost comedic sense.
"Number 5 just cries a river a minute,
7 wants to tie you up and drown you in it,
14 just wants to say so long, bygones,
32 wants to do things to you that'll make you blush,
10 would key that El Camino that you love so much,
And there ain't nobody wants to mess with 23.
Yeah, lucky 4 you, tonight I'm just me."
Cage9's song "My Doppelganger" (a.k.a. "Doble Opuesto") is about a guy who hurts his girlfriend (and possibly other people) via his other half, and apparently doesn't seem to understand it's himself until later in the song.
Naoki Maeda has so many aliases, he puts Renard to shame. 180, 190, 190', 200, 270, 290, RevenG, Re-Venge, Black Hole, White Wall, NW260, NM, Omega, Z, ZZ, sonic-coll, Neuras, and so many others. There are at least 50 at last count.
Eldar from Warhammer 40000 cultivate separate personae for wartime and peacetime so that they do not lose themselves to their bloodlust. The dang things are scary when they get pissed...
Call Of Cthulhu supplement The Asylum and Other Tales, adventure "The Madman". An investigator is driven insane by exposure to the Cthulhu Mythos and develops an evil alternate personality.
In Planescape the elvish spy Farrow has 15 personalities — each a devout member of a different one of the setting's cutthroat factions.
In the Ravenloft campaign, there is Malken, the Darklord of Nova Vaasa. His original personality is Sir Tristen Hiregaard, a nobleman who is not actually evil (listed as Lawful Neutral on his character sheet) and actually perceived as benevolent by some people (it depends on who you ask). However, a dark curse transforms him into a brutal killer called Malken whose victims are often the people Hiregaard himself cares about. No-one in Nova Vaasa, not even Hiregard himself, truly knows Malken's identity (although he suspects a dark presense inside him, and often orders his servants to lock him his rooms when he feels it; Malken is cunning, however, and usually escapes).
In GURPS a character may be created with multiple personalities. Depending on the "point value" of each personality (they may have different abilities), this can actually count as an advantage! The trigger is a roll against IQ in a "stressful situation"; fail the roll and switch personalities. (If you have more than two, the new one is chosen at random.)
In Orpheus, one of the Flatliners is Jeffrey Rose, a serial killer with no less than seven other personalities, and each one of them a serial killer in their own right. Making matters more complicated, after Rose's death, his ghostly form develops yet another personality, though at least this one is dedicated to killing Spectres.
Sora from Kingdom Hearts has multiple personalities. Sora himself is largely unaware of them, being Locked Out of the Loop to an epic degree, although he can sometimes sense their feelings. The other personalities are dormant and very rarely affect his behavior.
This also happened in the Space Ace video game (which later became a short-lived cartoon). After being struck by the bad guy's "Infanto-Ray", Ace would sometimes involuntarily transform into Dexter, a skinny, nerdy, teenage alter-ego.
In Final Fantasy VII, the protagonist Cloud suffers from a case of split personality, where thanks to Mako/Jenova experiments at the hands of Hojo lead to the Jenova cells injected inside him taking over his brain and creating a new persona based on Cloud's desires about being a Bad Ass SOLDIER operative like his idol Sephiroth and his friend Zack. The real Cloud is reduced to a mere voice in his head.
One of the villains in Xenogears turns out to be an alternate personality of the main character, created as a coping mechanism against his childhood abuse. The villain's name, "Id", offers a vital clue to those with knowledge of psychology. Notably, neither the main character nor Id are the original personality (and the situation only gets more complicated once reincarnation's thrown into the mix).
Xeno Saga Episode II also has a mini-boss who alternates between two personalities, one of which is cold and cruel, the other of which is hot-blooded and nasty. Oddly enough she doesn't feature in any story sequences and is just a throwaway boss.
In Killer7, the player-controlled character actually has seven distinct personalities, with their own looks, special abilities, everything. There's even a personality that's albino, one that's paraplegic, and one that's a woman.
In the first versions of killer7 the physical body that everybody else sees is Garcian's. There was either a cutscene or just a part of a level that showed this when Dan walked into a bathroom and saw himself Garcian. This is also alluded to in the released game when confronting Curtis Blackburn when he says "you turned into a badass"
In the ending, everything you knew about the split personalities is all torn down. They aren't Harman's split personalities. They're Garcian's, with the weapons of the six recessive personalities in Garcian's suitcase. Also, "Garcian Smith" is a more literal split personality of Emir Parkreiner, the most powerful assassin in the world, so powerful that a god's avatar says that he's not even a mortal being anymore.
Ford Cruller suffers from this due to a battle that shattered his psyche in the past and is only able to remain stable within his underground sanctuary, which houses one of the largest psitanium deposits. His personalities are all named Cruller and serve as several different roles in the camp, ranging from Ranger Cruller, Admiral Cruller, Chef Cruller, and so on.
Fred Bonaparte and his split personality Napoleon Bonaparte — Fred knows he's crazy, he just can't seem to get rid of Napoleon until Raz helps him out. (Crosses over with Genetic Memory).
Super Robot Wars Original Generations: In Mugen no Frontier: SRW OG Saga, Lamia Expy Aschen Brodel has personality split disorder. Just wait until she reveals some skin, and all the stoic android facade gets replaced with a Genki Girl personality.
Sheogorath, the Daedric Prince of Madness, is A split personality of Jyggalag, the Daedric Prince of Order. When all the other Daedric Princes realised how powerful Jyggalag was becoming, they used their vaguely established powers to curse him to become the very thing he hated the most.
The Shivering Isles in Oblivion contains a village called 'split' where each citizen has been turned into two people based on their Manic and a Demented sides.
In Portable Ops: Twins Elisa and Ursula are in fact one and the same.
Crying Wolf of Metal Gear Solid 4 suffers from a split personality. The "wolf" personality has a compulsion to murder children and the "crying" personality mourns those killed by the "wolf", but seems unaware that she is the "wolf".
Screaming Mantis. The mantis persona was created by her psyche to justify the cannibalism required for her survival.
Socks, the lunatic boxer from Facebreaker has two personality (a nice, English-accented intellectual .and an angry psychopath) which manifests in the sock puppets that he uses for boxing gloves.
A pirate appears in Escape from Monkey Island who has developed two additional personalities in order to cope with having his ego shattered by the Ultimate Insult. They are manifested through the puppets he wears in a Punch and Judy type of show, which themselves take on the forms of the series' hero and villain in appearance, though not so much in personality.
Tira, from has had her brain broken by prolonged exposure to Soul Edge, and she flips back and forth between her original "joyous" personality (where she'll kill you with a smile on her face) and her "malicious" one (where she'll just kill you).
Siegfried, before Nightmare could fully take over (and before Nightmare became a completely separate entity) Siegfried and Nightmare were sharing one body and Siegfried would usually wake up covered in blood.
Therese and Jeanette Voerman from Vampire: The Masquerade - Bloodlines. You never get the whole story, but the conversation you have with them after the fight in the diner suggested the split either happened when Therese was sexually abused by her father, when their father shot himself/was shot by Therese, or after they were Embraced by a Malkavian.Word Of God is that the writers carefully researched DID in order to maintain the arc's plausibility. And considering that the Malkavian Madness Network works like a very unusual kind of Hive Mind, it can't be entirely ruled out that they actually did start out as twin sisters, one of whom didn't physically survive Embracing.
In Clock Tower II: The Struggle Within, the entire storyline is based around a girl who has a malevolent split personality.
Emil Castagnier from Tales Of Symphonia Dawn Of The New World. Normally, he's very timid, sweet, and cowardly. But when he goes into his humorously named, "Ratatosk Mode", he turns much more vicious and merciless. Though, he is actually Ratatosk, and "Emil" is actually a fabricated personality, but still...
Eternal Darkness' Xel'lotath speaks in two voices - one is well-spoken, rational-sounding, and almost as imperious-sounding as the paper to her scissors Ulyaoth. The other sounds extremely paranoid and somewhat delusional, always using a quiet but harsh whisper. And with the remarks each voice makes, it sounds like she could hold a full-blown conversation with herself. Suitably, she is the goddess of insanity.
Sakubo, a character of .hack/GU, has a serious case of this. Originally stating he and his sister shared a character, we later find out they share the character. Saku, the girl side, is the more violent side and Bo, the actual person, is a shy boy who developed Saku to help him stand up for himself. It's essentially like sticking Blackrose and Elk into one body. Add in the fact that Saku is obsessed with 'White Haired Pretty Boy' Endrance and things get a little weird if you think on it too long...
Dinah, one of the spirits from Summon Night: Swordcraft Story 2 has a Good Angel, Bad Angel split personality. The "bad angel" personality is the default one, though sometimes her "good angel" side will shine through every now and then to apologize profusely for Bad!Dinah's rudeness.
Tink from Disgaea 2 Cursed Memories has two sides - the "blue" personality, which is calm, polite and timid, and the "red" personality, which is lecherous, short-tempered, rude and selfish. It takes a magic spell to suppress his "red" side in the cutscenes, though he can switch between them freely in actual gameplay. When in the "red" side, he gets a boost to his stats by being near female characters.
Agent Francis York Morgan of Deadly Premonition often has conversations with "Zach", to the confusion of others. Near the end, it's revealed that Zach is the original personality and York was developed as a child in order to protect Zach's psyche. Eventually Francis York Morgan goes back to being Francis Zach Morgan in order to confront Forrest Kaysen for the finale.
Ethan from Heavy Rain experiences occasional blackouts, and he believes that these blackouts occur when his alternate personality (who he believes is the Origami Killer, who is responsible for kidnapping his son) takes over. The actual Origami Killer is a completely separate character, and there's no real explanation given for Ethan's blackouts.
The reason behind Ethan's blackouts could be both the trauma he suffered from the accident he had trying to save Jason, or the stress caused from it. That and since the Origami Killer has been over the news recently, he could have (unconsiuosly) attempted to find a way to blame himself for something.
Zoya, Pontius, and Amadeus from Trine probably don't count, since they're three separate people bound to an artifact that lets only one of them exist at a time, not three personalities in one body. But it's similar.
Inazuma Eleven 2's Fubuki Shirou has a special mention of a Split Personality aside from other characters with dual modes. His regular persona, a soft spoken and timid defender, and his alter persona, created from a memory of his dead brother, a Hot Blooded and reckless forward. The issue is developed further in the story.
GO has Kariya Masaki, who acts sweet generally except to Kirino; which is hinted to be his true nature.
Gemini from Sakura Wars (Sakura Taisen 5) seems to be pulling a not-very-convincing masked vigilante act, until it's eventually revealed that she has a sister Geminine... living inside her.
The ren'ai game Ori, Ochi, Onoe is a rare instance of two people having a love triangle or in this case, rectangle.
The Fallout New Vegas DLC, Dead Money, introduces Dog/God, a Nightkin with split personality. Dog is the dumb, violent, Extreme Omnivore who obeys Elijah's every whim and brings victims to the Sierra Madre to help him break in. God is exceptionally intelligent and well-spoken, but very cold and calculating and regularly threatens the people he's with. Dog comes out when a recording of Elijah's voice is played, and God comes out with a recording of his own voice. In the end, Dog attempts to commit suicide and the player can kill him or talk him out of it, which allows for him to encourage one of the personalities to take over or merge both of them into a single balanced being.
Mystery Trackers: The Void involves the sinister events following the disappearance of Marius Void and his criminally-inclined "brother" Sirius.
Goal gets a variation on this in Chaos on Deponia - Her mind was stored on hard-disk-like brain implant, but after some Rufus-related shenanigans the data on it is split into three disks, each of which contains a third of Goals personality. Rufus can use a remote control to flip Goal between her selves. Tuning in the right Goal for the right situation is a core mechanic of the game.
In Borderlands 2, Krieg suffers from this as a result of the experiments Hyperion put him through to make him such a deadly killing machine. His dominant, active personality is a lunatic, buzz-ax-swinging berseerker who spends most of his time spewing jumbled nonsense (i.e. trying to talk to Maya resulted in him screaming "I'M THE CONDUCTOR OF THE POOP TRAIN!" at the top of his lungs). The other side of him is a much more sane and moral inner voice that tries to steer Krieg's murderous impulses into targets deserving of their wrath, but who has a hard time controlling the insane half of his mind.
Miku in A Profile claims this, but Kaine claims it's incredibly unlikely because not only is DID extremely rare, but her behavior simply doesn't match up to what it should because the claimed personalities are aware of each other, which defeats the whole point. He's mostly right, but not entirely.
The personalities of Yasu aren't so much actual split personalities than a cross between imaginary friends and idealized personas. Shannon was originally an Imaginary Friend to Yasu, who also represented the ideal of a perfect servant that Yasu wanted to achieve, until Yasu decided to be a witch instead and created the Beatrice persona. Later, when Yasu as Shannon began to suffer from waiting for Battler to return to Rokkenjima, she created Kanon as an imaginary little brother and later took on the Kanon personality for real, while also transferring the love for Battler from Shannon to Beatrice. The personalities are all able to speak to one another, representing the conflicts in Yasu's heart. The main conflict is that three different people are each in love with one of Yasu's personalities.
Rosa is seen by her daughter Maria as having one in order to justify her abusive behaviour, interpreting her mother's violent mood swings as being possessed by a "Black Witch".
In Remember 11: The Age of Infinity, Keiko Inubushi suffers from Dissociative Identity Disorder, resulting in her being sent to the SPHIA psychiatric hospital when one of her personalities commits several murders. Later, protagonists Kokoro and Satoru allow their companions to believe this about them (They are actually undergoing a series of Freaky Friday Flips, but find that its easier to convince their companions "I have two personalities", rather than "My mind randomly switches with somebody else's").
In Dangan Ronpa, Genocider Syo, an infamous serial killer, is the split personality of Touko Fukawa. Despite this, Genocider Syo doesn't actually kill anybody during the course of the game, despite being suspected twice as a murderer. The personalities switch when one of them sneezes, and they don't share the same memories. As you can imagine, they're both very different people: Touko is gloomy and pessimistic, while Genocider Syo is a gleefully sadistic Large Ham. About the only thing they have in common is their infatuation with Byakuya Togami.
Lisianthus of Shuffle absorbed the soul of her unborn sister while still in the womb. The two take turns being the dominant personality. In the original visual novel she has no name but is known as Reverse Sia. Giving her the name Kikyo becomes a plot point.
In Ace Attorney, Ben and Trilo seem to have something similar to Batman's Ventriloquist, in that Ben's doll Trilo acts as if it has a mind of its own and routinely beats up its owner. Trilo also seems to forget he's a doll at times - at one point, he tries to get Ben to sing with him in a round.
Tohno/Nanaya Shiki from Tsukihime, with a twist: despite barely appearing, the Nanaya identity (his Super Powered Evil Side) is actually his original self, the Shiki who would have been had the events of Tsukihime's backstory not occurred. His "main" Tohno identity was added after "the incident" via brainwashing, but it remains as his main identity even after he finds out the truth.
In the relatively unknown webcomic Jix, the titular character is the second personality of an invader, Remula, from an alien race who was surveying Earth. She stayed on Earth until she was sane again. She's manifested two more personalities since then, Lamerix the Mad Scientist and (male) superhero The Ambis.
Kano, the protagonist of Kagerou has several personalities. The personality that answers to "Kano" is initially not aware of the others.
Mountain Time has Donna the Bears, who has multiple personalities that are all bears.
Repeated transformations into a mind-altering form seem to cause this. For example, the 'Lilly amulet' causes the wearer to turn into a slightly hyperactive gender-bent child. At the beginning of the comic, the minds of Evan and Lilly are separate (Evan is gone while turned into Lilly, and vice versa) except for one incident where their minds were switched. Lately, however, Lily seems to be present even while Evan is himself. Similarly, while the Jason-Sonja transformation was a simple Gender Bender, they seem to be diverging slightly as Sonja gains time existing.
Weres seem to be similar, with the normal form and were form having separate minds (e.g. Yukio/Yukiko). Samantha and Katie are exempt because of the amulets that specifically suppress the were-mind and leave the normal mind in control, to the extent that they never developed separate minds in the first place (Though Katie transformed once or twice without the amulet, all examples of multiple-personalities were developed over multiple and/or long-lasting transformations).
Myrh (formed when magical slime ate Lord Sykos' maid) goes through a short time with this when a mind-meld with Ming and some jellybeans cause her human and slime portions to rebel against each other, as the slime attempts to become Ming.
There's also Gamzee, though in his case there seems to be three personalities: a 'good' host personality, which is kept dominant to begin with by Sopor slime and two 'evil' (or rather, sociopathic) alters.
Gemini is a slice-of-life about Bernie and Z, and their life as multiple (and Z's transgenderism)
Chelsea Grinn of Chimneyspeak has four, progressively less sane, personalities.
In Moon Crest 24, Derek and Dwayne both have the spirits of Drake and Daniel inside them respectively. And while Dwayne and Daniel are aware of eachother, Derek and Drake are not.
Merry, in the Whateley Universe, has four personalities: Chaddy, her more innocent child self; Chad, her cynical, distrustful, early adolescent self; Merry, the most normal one and the dominant personality; and Mai, an evil AI she defeated that took up residence in and merged partially with her mind. Eventually these four were separated into pairs when Merry got accidentally cloned; Chad and Chaddy now live in Petra's head, while Merry and Mai now live in Paige's. And to those of you wondering why two of those personalities have male names . . . it's the Whateley Universe. Figure it out. Fey, meanwhile, doesn't so much have a Split Personality as she actually has another person in her head, specifically Aunghadhail, an ancient Sidhe queen who died millenia ago but is now Back from the Dead, sort of.
Flippy from Happy Tree Friends has an Axe Crazy personality called Fliqpy, although his problems sometimes resemble regular Schitzophrenia, with his PTSD as the trigger.
Wishing Star was recently reveled to have this in the form of Dark Star.
Kaleigh Jones from v1 of Survival of the Fittest had two, in the form of child-like "Carly" and nymphomaniac "Freya". Bizarrely, Kaleigh seemed capable of deciding which of her personalities was in control and when.
Played seriously with the "evil" personality of Two-Face almost completely consuming the mind of Harvey Dent to the point where the "good" personality rarely surfaced again, much to Batman's dismay. This got taken to a weird extreme when the killer vigilante "The Judge" appeared and started trying to kill Batman's rogue's gallery, including Two-Face, with death traps. The Judge turned out to be an alternate personality of Two-Face himself, who had no idea that he was the same person.
"Father": We're actors, remember? You cancelled our show because you whined you weren't getting enough attention!
Baby Doll: But I knows now I made a boo-boo! (as Dahl) It was hard for me out there. I studied and trained and auditioned, but no one wanted me. Over the years I remembered how happy I was with all you around me, and the folks at home watching me each week... Me. (as Baby) Baby Doll. Hee hee! Now I'm Baby for good, and everyone will love me again!
And then there was the Ventriloquist and Scarface, the latter of which was a separate personality of the former, embodied in a ventriloquist dummy with a machine gun. Both personalities are present at the same time, it's just that the Ventriloquist can't acknowledge that he's the one working Mr. Scarface and giving him voice rather than the puppet being his own person. This clearly seen where Scarface sleeps in a lavish bedroom, and the Ventriloquist sleeps in a closet. It's occasionally hinted that Scarface has a will of his own, but that's just silly.
The Batman takes this even further: Scarface's ventriloquist is "Reformed" by being given a new puppet meant to be a "Good" alternate personality. And it works, too: the new puppet even gives Batman the hint that Scarface is on the loose again.
The Batman The Animated Series version of Scarface episode went so far as to describe the Ventriloquist and his dummy as two separate people who were born trapped in the same body, with Batman making an analogy to Siamese twins. Split Personalities Do Not Work That Way, to put it mildly, but the series did go on to provide a more realistic portrayal of Dissociative Identity Disorder with Two-Face, whose personalities are different facets of Harvey's mind.
In the earlier seasons, Mr Garrison's hand puppet Mr Hat was his other personality and imaginary friend that helped him to deal with sexual abuse and transexual thoughts. Said in "World Wide Recorder Concert":
Mr Mackey: Mr Garrison, are you alright?
Mr Hat: Mr. Garrison isn't here right now...
Mr Mackey: Mkay, Mr Garrison, you're just having a hard time dealing with the memories of your father's sexual abuse, so you've switched personalities to Mr Hat.
Mr Hat: Ooh, good one Sherlock, you figured out all that by yourself?
However, as is later revealed, Garrison feels traumatized by the fact his father didn't molest him.
Parodied in the episode "City Sushi" where Dr. Janus diagnoses Butters with multiple personality disorder, identifying Postman Butters, Fireman Butters, Big Rig Butters, Inspector Butters, Porn Star Butters, and Professor Chaos. Meanwhile, Janus in fact does have other personalities. Janus has four personalities in total: himself, Billy, a young boy, a violent, unnamed criminal, and Lu Kim, the owner of City Wok, who in the end becomes the dominant personality.
Blitzwing of Transformers Animated, with a face to go with each personality. Blitzwing's weaponry and vehicle modes seem to be tied into his personality (in the only interpersonality conflict he's had so far, his angry and calm faces argued over which vehicle form to scan). The calm face uses some sort of ice missile and a jet form, while the angry face uses a flamethrower and tank form and the crazy face seems to be able to use both - but is not as skilled with either. Prowl actually caught on to this during a battle, and used Bumblebee to annoy Blitzwing so much that he switched from calm/jet to angry/tank—and promptly fell out of the sky.
Word Of God gives the personalities the names of Icy, Hothead, and Random respectively.
Blitzwing's personalities technically aren't different people; they're just immediate shifts between certain states. As seen in the falling tank incident, he'll often swap depending on his mood/the situation—you'll never see Icy get angry or Hothead act happy. Though there is the infrequent time that the three states interact with each other as if they were separate people. They once even debated over a vehicle mode choice:
Icy: Ze jet. Hothead: Tank! Icy: Jet. Hothead: Tank! Random: Ooh-ooh! Why not scan both?
Dr. Rockso, the Rock n' Roll Clown (he does cocaine) in Metalocalypse. Dr. Rockso is the dominant personality, but amicable troublemaker Leonard Rockstein briefly succeeded in suppressing him just long enough to make his return all the more surprising.
Parodied in the Soap Within a ShowAll My Circuits in "Beast With A Billion Backs," as Calculon discovers he has a fourth split personality. And that it's having an affair with Monique behind his main personality's back.
In the episode "Insane in the Mainframe," Fry encounters a robot Abraham Lincoln in the robot asylum. The problem isn't that he thinks he's Lincoln, but that he has multiple personalities, all of which are Lincoln.
"I was born in 200 log cabins."
Dr. Splitz/Splitzy in Captain Simian And The Space Monkeys. Apart from his Meaningful Name, he's also notable in being The Smart Guy. Sort of. Dr. Splitz is incredibly intelligent and ingenuous, while Splitzy is an impulsive moron. However, they both seem to share incredible knowledge of electronics and machinery, and Splitzy's irrationality sometimes comes in handy when Dr. Splitz is hesitant.
They also actually go back and forth between acting like one person with two personalities and interacting with one another.
Dr. Splitz: Uh, don't you have anything to add, Splitzy?
Splitzy: I ain't talkin' to you!
Ace Lightning has Random Virus, a cyborg with one good and one evil personality. He's constantly fighting between them though how much these two sides of him are indivdiuals is unclear.
In Beavis And Butthead, The Great Cornholio makes his appearance whenever Beavis has too much sugar and/or caffeine, and when he comes back to himself (usually in some awkward situation), he doesn't remember Cornholio's actions.
Total Drama Island's season four cast features Mike, labeled the Multiple Personality Disorder, who has four alternate personalities that even have their own names:
Lampshaded/played with in The Mask episode... Split Personality. The character is already two personas in one, but subverts the trope as the second personality can only come out when Stanley puts on the mask and changes. However, in this episode, the mask itself is split down the middle, and Stanley puts on one half. The results were... interesting, with half of his body changed into The Mask and the other half left alone. Both characters were sharing one body at the same time. This leads to some very interesting circumstances as Stanley has to try to hide this while half his body is changed. The other half of the mask? It gets worn by Stanley's old high school bully, who ends up with a psychotic murderous half that even manages to freak out the normal side.
Anne Heche claims (or at least once claimed) to have multiple personalities.
Herschel Walker was a former football player with tons of personalities, for instance, The Hero and The Professional White Man.
Kenneth Bianchi, one half of The Hillside Stranglers, attempted to set up an insanity defence. He claimed to have another personality named Steve Walker and, according to Bianchi, Walker was the killer - Bianchi himself was innocent. He managed to fool a couple of psychiatrists before the whole charade collapsed.
There have been several autobiographies written by people with DID; for instance, The Flock: The Autobiography of a Multiple Personality by Joan Frances Casey and When Rabbit Howls by the Troops for Truddi Chase. Truddi Chase has also appeared on The Oprah Winfrey Show.
In an interesting phenomenon, virtually everyone self-diagnoses themself with this after hearing about the symptoms and problems related to it, so much so that it's mentioned in textbooks immediately after describing the phenomenon. This means that genuinely finding a real case is somewhat difficult, however it does mean that most people feel like they have conflicting personalities so there's a fine line between genuine DID and simply being a normal person.
There is a related condition - a mental event known as "disassociative fugue" - where the sufferer loses a large chunk of their history and wanders off with no idea of who they are. Some documented cases have established themselves in a completely different life from the one that they left. And it can occur ideopathically and spontaneously - i.e. with no known cause and with no warning. Fugue tends to be associated with some form of traumatic event, but doesn't have to be. Scared yet? Fortunately, it's very, very, very rare.
The "Society of Mind" hypothesis states that all humans are Mind Hives.