Jeanne-Marie Beaubier, a.k.a. Aurora of 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.
Lance Temple a.k.a. the Outlaw Kid developed this in Blaze of Glory after his Secret Identity gave his gun-hating father a heart attack. Now Lance Temple searches for the Outlaw Kid to avenge his father's murder, unaware that the face behind the Outlaw Kid's mask is his own. Even by the end of the series, he hasn't fully recovered, though the two wind up becoming a pretty badass Split-Personality Team for a bit there.
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's 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', blond 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.
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 in-between. Grant Morrison in particular is fond of the idea that the Joker has a unique condition where he has no "true" personality, but continually reinvents himself through multiple "superpersonas". (It's suggested by Dr. Adams in Arkham Asylum: A Serious House on Serious Earth, and the text story "The Clown at Midnight" in Batman (Grant Morrison) is largely a character study of it happening.) Chip Zdarsky makes this explicit in his Batman run with the story "Joker: Year One", which officially places Batman: Three Jokers in Canon Discontinuity and explained the three Jokers revelation in "Darkseid War" as the Joker is indeed one man, but the "three Jokers" thing is just him having DID.
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. Batman (Grant Morrison) reveals that Batman, who prepares for everything, 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 dependence 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.
Jean-Paul Valley has, at most, three. There's Jean-Paul himself, a timid mild-mannered man who has a thing for electronics, there's Azrael, a Super-Soldier with no scruples about striking down evildoers and an archaic sense of doing things and there's "Batman", who has Jean-Paul's smarts, Azrael's strength and zero compassion. The last one tends to appear under duress.
Jack Ryder sometimes sees the Creeper as a completely different personality.
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 they were the same person, even with his enhanced senses. (It seemed that the change even affected her body odor somehow.)
Shasti from Adam Warren's version of the Dirty Pair is an Artificial Human deliberately engineered with four personalities for different tasks.
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. Ms. Challis and members of her group were based on Truddi Chase and her Troops, authors of the 1986 book When Rabbit Howls.
Copycat from DV8, whose five personalities are each represented by different fonts and word balloons. For the record, those personalities are: Standard, overburdened teenager; "Spy", analytical and task-oriented; "Soldier", aggressive and combat proficient; "Nihilist", rebellious and troublemaking; and "Little Gemma", essentially Copycat as she was at age 6. 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.
Fantastic Four: The Invisible Woman has Malice, who was created by Psycho-Man taking advantage of Sue's vulnerable state after she lost her baby in childbirth.
G.I. 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 "Road Pig" and "Donald" are depicted as two distinct personalities: a Dumb Muscle thug and a Wicked Cultured sophisticate, respectively. 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. And the Trademark Favorite Food to all the Dreadnoks, chocolate covered donuts and grape soda.
The 2003 Human Target ongoing starts off with Christopher Chance, having taken the identity of late Hollywood movie producer Frank White full-time at the end of the last story, facing threats from an increasingly bold, obsessive stalker. At the climax of the issue, Chance discovers his stalker was... himself. His subconscious desire to shock his original personality out of "hiding" caused him to create an alternate identity to endanger himself and his wife. She doesn't quite believe that he had no control over this and leaves him. He cries when he finds the mask of the stalker's face — as he puts it, he's so good be fools himself.
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).note The Professor seems to be based on Billy Milligan's ability to voluntarily integrate everyone in his system; he called this state "the Teacher". Other multiples report being able to integrate at will and don't recommend it, agreeing with Billy that "the whole is less than the sum of the parts." Some sources have interpreted these personas as representing different stages of Banner's life; the Savage Hulk is the immature child who wanted to be strong enough to protect Bruce's mother from his abusive father, Fixit is the moody teenager Bruce never let himself be, and the Professor represents the adult amalgamation of all his other experiences.
Two other personalities in Bruce's lineup are the Devil Hulk (also called the Immortal Hulk), a reptilian creature created to be a violently protective father figure to Bruce; 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.
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.
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.
Betty Ross as Red She-Hulk. The degree to which she retains control over Red She-Hulk varies a lot. Sometimes it's just an angrier Betty, while at others it is an entirely different persona whom she fears losing control over.
When M.O.D.O.K. placed Doctor Samson under mind control it produced a split personality. This led to a powerless Leonard who was defined as the good one and an evil Samson whose abilities are greater than She-Hulk's.
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-Zero Hour 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 Threebot 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.
Moon Knight started off with the gimmick of having multiple secret identities. Depending on the Writer, this became a dissociative identity 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, the story is that he really is possessed by Khonshu, and his mind makes sense of this by constructing alternate personalities around Khonshu's various forms.
Ms. Marvel (1977): When the series starts, Carol Danvers and Ms. Marvel are two separate personalities, having been split when Carol was blasted by the Psyche-Magnetron that gave her powers. The 'Ms. Marvel' personality thinks she's a Kree warrior, helped by memories absorbed from Captain Mar-Vell, and neither knows about the other. However, as the series goes on, they do learn about the other, and the line between them starts blurring, the two even struggling for control over their body, eventually merging when a goddess points out the truth.
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.
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.
The Green Goblin sometimes suffers from this, though in an inversion, the real persona, Norman Osborn, can be just as evil as his Superpowered Evil Side.
Also the Lizard, who is Bruce Banner-lite.
Doctor Octopus sometimes showed signs of this in his career. There were times when his original, timid, benevolent personality of Otto Octavius would resurface, but his evil Doctor Octopus persona would always return. (In the movie Spider-Man 2 this Trope seemed to apply even more.)
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.
Transformers: Generation One features an Autobot character called Punch, who displays the unique ability to transform into a second robot mode, which he uses to become a mole in the Decepticons called Counterpunch. Over time Counterpunch develops into a second personality. Also qualifies as Becoming the Mask.
Wonder WomanVol 1: The Silver Age Cheetah Priscilla Rich was a wealthy but troubled socialite who suffered a psychotic break, and a dual personality developed. Her new personality was very different from her normal reserved self and donned a cheetah costume to fight Wonder Woman in the 1940s.
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).
Professor X himself has a bad history of every negative feeling he's tried to repress forming a personality of its own. Times have included during "The Phoenix Saga" (when, while not fully recovered from his nightmares about he was Lilandra's fight with her brother and a fight with Firelord resulted his dark side lashing out at the X-Men with mental projections of the original team while Xavier was knocked out),The X Men Men And The Micronauts mini (where, as "the Entity", it tried to conquer the Microverse), and Onslaught (where his dark side merged with the basest part of Magneto's mind after mindwiping him in Fatal Attractions (Marvel Comics) to become the titular villain).
