[[quoteright:250:[[Film/DrJekyllAndMrHyde1931 http://static.tvtropes.org/pmwiki/pub/images/ChangingImage_4791.jpg]]]]

->''"I guess we're all two people. One daylight, and the one we keep in shadow."''
-->-- '''Bruce Wayne/Franchise/{{Batman}}''', ''Film/BatmanForever''

When a character and his EvilTwin, EvilCounterpart, or ShadowArchetype are really the same guy after all. Or, sometimes, a completely different character is [[TwoBeingsOneBody sharing body space]] with another. The point is, the villain [[EnemyWithin lives inside the hero's body]], and therefore hides in plain sight. The hero is trying to catch himself.

If the two personalities are aware of each other, it becomes a case of GollumMadeMeDoIt. For a more mundane version, see MoodSwinger. See InVinoVeritas if the change is alcohol-induced. As the Hyde personality's crimes are outside the character's control and, often, the character is unable to stop themselves from becoming evil, this is often a case of being DrivenToVillainy.

Sometimes they're not really [[DarkIsNotEvil evil]], although ... see DrPediaAndMrTrope for the {{Wiki Trope|s}} version of this. Occasionally, this can be resolved (not necessarily favorably) with a SplitPersonalityTakeover, or with a SplitPersonalityMerge that reconciles both sides into a healthy whole. Also, the "Jekyll" side isn't necessarily "good" either.

Comes, of course, from ''Literature/TheStrangeCaseOfDrJekyllAndMrHyde'', by Creator/RobertLouisStevenson. It used to be a TwistEnding, but it [[AllThereIsToKnowAboutTheCryingGame no longer surprises anyone]]. Most adaptations of the work focus on said twist.

The real life example of [[http://en.wikipedia.org/wiki/Deacon_Brodie Deacon Brodie]] (cabinet-making pillar of the church by day, burglar by night) is said to have inspired Stevenson, as did the story of [[https://en.wikipedia.org/wiki/Horace_Wells Horace Wells]], a pioneer of medical anesthetics. While researching chloroform by [[ProfessorGuineaPig testing various dosages on himself]], Wells unknowingly built up a dangerous level of the drug in his system, and ultimately attacked two prostitutes with sulfuric acid in a state of intoxicated paranoia. He then committed suicide after sobering and learning of what he had done.

Not to be confused with the stage musical [[Theatre/JekyllAndHyde of the same name]].

Since the fact that the hero and the villain are the same person could often be used as a twist ending, beware of spoilers on this page.



[[folder:{{Anime}} and {{Manga}}]]
* Kenshin and Battousai in ''Manga/RurouniKenshin.''
* Kyo and Kyoshiro in ''Manga/SamuraiDeeperKyo.'' [[spoiler: Subverted in the manga, played straight in the anime.]]
* Tsubasa from [[Anime/MetalFightBeyblade Beyblade: Metal Masters]] has a dark side when he beyblade battles, making him obsessed with winning, going a bit mad. (He usually loses as a result)
* ''Anime/MagicalProjectS'': Misao Amano's normal self is that of a stereotypical ShrinkingViolet [[FriendlessBackground friendless]], [[ShyBlueHairedGirl blue-haired]] IllGirl. However, this persona falls away when she's transformed into Pixy Misa, the manifestation of her deeply repressed id: an egomaniacal [[GreenEyedMonster jealous]] DarkMagicalGirl [[VillainousHarlequin trickster]].
* Inverted with Lucy/Nyu from ''Manga/ElfenLied''. Lucy, the evil counterpart, is actually the original character (sort of), while a blow to the head caused her to go into [[CuteMute passive, non-lethal "Nyu" mode.]]
* After the protagonist of ''Manga/DeathNote'' pulls a MemoryGambit, he devotes himself to catching Kira, not being able to remember that he himself is Kira. The instant he regains his memories, he reverts to his original personality and begins killing once more.
* ''Anime/{{Gankutsuou}}'' has Literature/TheCountOfMonteCristo possessed by the titular demon which completely submerges his original good personality as Edmond Dantes.
** This is only a part of the story, as it was Edmond's own lust for revenge that summoned Gankutsuou to him, to begin with, and Gankutsuou has no personal interest in doing any harm to Edmond's enemies or their loved ones, only fulfilling his own end of the bargain. When it seems that Gankutsuou has fully consumed Edmond, he simply walks away from the person he was about to kill as revenge by proxy, without so much as looking back.
* ''Anime/{{Mnemosyne}}'' subverts this in its penultimate episode. Rin, who was sucked into a jet engine, and presumably [[EasyAmnesia got her memories mixed up from having her brain turned into a shake]], is seen working at a MegaCorp by day and killing other immortals and collecting their time spores by night. [[SideKick Mimi]] even lampshades it. However, it turns out that [[spoiler:the latter was actually [[TheRival Laura]] in a cyborg body designed to look like Rin.]]
* In ''Manga/DGrayMan'', this is the case with Tyki Mikk and quite possibly the rest of the Noah.
** Nah, just Tyki (who 'loves humans'); but his mind remains constant between sides, and he gave his little friend the silver off a murdered exorcist's coat as a present. If Allen ''had'' gotten it, the plot might have run a bit differently....
** Also, White Tyki appears to be effectively dead. His identity took a serious scramble back when Allen thought he'd cut the evil out of him and got a ''[[SuperPoweredEvilSide really ]]''[[SuperPoweredEvilSide superpowered ]]''[[SuperPoweredEvilSide especially ]]''[[SuperPoweredEvilSide evil side]] instead. Surprising pulled himself back together, but he's different.
** The Noah are activated out of normal humans, whenever a seat is left unfilled by a death in the family, and for the most part memory is not continuous from incarnation to incarnation, but those persons are still subsumed into the Noah identity once activated. [[spoiler: This is one of the things Allen is trying to prevent happening to him.]]
*** Whether [[BigBad Adam the Millennium Earl]] and the Fourteenth have died and recorporated before is not clear; very possibly they haven't. Road is over thirty five now; it's possible Adam has kept that rakish young face for thousands of years. (And covered it with a grinning balloon thing in a goofy hat about as long. Mysteriously.)
* ''Anime/{{Hellsing}}'' has Yumiko Takagi, sweet and gentle nun, kept on hand by the Vatican's secret team of assassins for her alternate personality Yumie, who is a berserker killing machine (and darn good with a katana).
* Harumi Chono from ''Anime/ParanoiaAgent''. Tutor for Ichi by day, a prostitute named Maria by night. The way they communicate with one another? Leaving messages on their answering machine for each other.
* Allelujah and Hallelujah in ''Anime/MobileSuitGundam00''.
* ''Manga/ZettaiKarenChildren'' has [[LawfulEvil Mirage]], who is also [[ChaoticEvil Phantom Daughter]]. Both personalities are hiding in and from Yuuri, AKA The Doll, an ordinary schoolgirl "built" for infiltration [[BecomingTheMask that they are spending an increasing amount of time in]], to their boss' displeasure. Additionally, there's a ''fourth'' personality that the other three are unaware of.
* In ''LightNovel/{{Kampfer}}'', Akane is a sweet, shy, bespectacled girl who often hangs out in the library. When she turns into a Kämpfer, then she becomes a real mean, foul-mouthed, trigger-happy bitch with a pair of pistols.
* In ''Manga/ProjectARMS'', [[spoiler:Keith Black has his original, rather sweet personality and is gradually [[GrandTheftMe taken]] over by his "father" Keith White, who is a demented maniac [[AGodAmI with a God complex]]]]. Alice herself is split into "White Alice" and "Dark Alice".
* ''Manga/{{Inuyasha}}'':
** Naraku and his evil human self, Onigumo.
** Suikotsu and his evil personality.
* In the manga ''Manga/SixSixSixSatan'' (or ''O-Parts Hunter'' in the US), the main character Jio has Satan inside of him. Satan comes out when Jio's or his friend's lives are threatened. [[spoiler:That is, until the time skip. By the end, it's revealed that Jio is Satan reborn. Jio is ''Satan's'' dual personality.]]
* ''Manga/RosarioToVampire'' has Moka Akashiya, a shy, well mannered girl who is not always confident. Her true self is a thuggish brute of a vampire who can kick the snot out of anyone.
* ''Amuri in Star Ocean'' has Perrier/Vernier La Mer. Perrier is the real personality who, as a result of torturously cruel parenting, subconsciously created Vernier as a defense mechanism and referred to her as her older sister. When seeing her reflection, Perrier would see Vernier looking back and talking to her, always taunting and insulting her. Vernier does not take full control of Perrier, though, until she is pushed into a state of extreme terror.
* Jūgo of the Scales in ''Manga/{{Naruto}}'' is a GentleGiant who lives in constant fear of what he will do when his bloodline transforms him into his [[TheBerserker Curse Seal self]].
* ''Manga/OnePiece'' gives us Cavendish; When awake, he's a gentlemanly Bishounen of an AttentionWhore. But when he falls asleep, his SuperPoweredEvilSide Hakuba takes control, and goes on a violent spree so fast that no one can see him. Unfortunately, he also has a bad tendency to fall asleep in the middle of the day.
* ''Manga/YuGiOh'' has Marik and Yami Marik, the latter being the personification of Marik's rage and anger. He eventually hijacked Marik's body and tried to kill his other self to maintain complete control.
* In ''Anime/YuGiOhCapsuleMonsters'', the Millennium Ring split Alexander's soul into two halves, one his peaceful side and the other his war-mongering side. The evil side notes that without him Alexander could have never conquered half the globe.

[[folder:Comic Books]]
* ''Franchise/{{Batman}}'':
** Harvey Dent, a.k.a 'ComicBook/TwoFace' has this going on as well, with the split represented by Harvey's own split face; his unblemished, handsome right side representing the good, noble District Attorney Harvey Dent, and the scarred, mangled left side representing the malevolent, vicious criminal Two-Face. In his case, the choice between 'Jekyll' and 'Hyde' depends on the results of a coin toss, with good or bad triumphing depending on which side the coin comes down on.
*** This is singly most obvious in his debut appearance, where distinct similarities are drawn between him and the story. In fact, his appearance was inspired by [[http://about-faces.livejournal.com/6931.html a poster for the Spencer Tracy film]].
** ''ComicBook/BatmanTheDarkKnightReturns'' turns this on its head. [[spoiler: Recent breakthroughs in plastic surgery have restored his face to normal, but at the unforeseen cost of forever destroying the "Harvey" half of his personality, and permanently leaving the "Face" in complete control.]]
** The Ventriloquist and his puppet, Scarface. Thought most people (including some writers and readers) act as if Scarface were actually alive.
* ''ComicBook/GreenLantern'':
** Kyle Rayner's vast powers were not being fully harnessed, so they formed a shadow entity called Oblivion.
** Hal Jordan had an arc where his...conjured body was warping between Spectre, the white-templed Evil Hal run by the fear entity Parallax, which is what he looked like when he did the genocide thing, and his own mixed-up personality, which looks like he did when he was a spry young pilot and at the top of his superheroing game. Often the head and shoulders of one entity will come thrusting out of one of the others. It verges on [[{{Squick}} squicky]]. They argue a lot. Specter only possessed Hal hoping he could purge Parallax, but now it looks like Parallax might just be getting the Specter's considerable powers, and the Specter and Hal can't see eye-to-eye enough to work well together.
*** Ultimately Parallax is overwhelmed, the Spectre [[BlueAndOrangeMorality ditches Hal to go find another host]] just when it looked like they could really beat Parallax, the remaining two split, and Hal winds up back in his body (which had been preserved where he sacrificed himself in the sun), which de-ages to match the look of his soul, and he's a good guy again. Just in time for the world to go to hell.
* The original ''ComicBook/{{Eclipso}}'' had Bruce Gordon at war with his evil alter-ego, Eclipso. Later retconned with Eclipso to be a separate entity trapped in a black diamond that posses his user.

* Bruce Banner and his more famous dark side the ComicBook/IncredibleHulk. This has been played with many times over the years, with Hulk varying from a brutal monster to an innocent savage. For a while between ''ComicBook/WorldWarHulk'' and ''Hulk: Agent of S.H.I.E.L.D.'', Banner was portrayed as ''Hulk's'' dark side, since [[spoiler: unlike Hulk, he'd actually killed someone]].
** In the ''ComicBook/{{Marvel 1602}}'' {{Elseworld}}, David Banner gets transformed into the Incredible Hulk. Lord Banner works as an enforcer for [[UsefulNotes/TheHouseOfStuart James VI of Scotland and I of England]], and is evil, sadistic and altogether not a nice bloke at all. Follow-ups reveal that the Hulk, on the other hand, is noble and intelligent. (And his influence eventually redeems Banner.)
* ''ComicBook/SpiderMan'':
** The Green Goblin is sometimes, and to an extent originally, depicted as a split personality of the milquetoast scientist ComicBook/NormanOsborn. The main difference is that Osborn is a ManipulativeBastard, while the Goblin is an AxCrazy psychopath. Since he came BackFromTheDead, Osborn had been more or less in control and became the Goblin willingly and [[ForTheEvulz for shitz and giggles]], but recently he's started losing it again.
*** When he had a breakdown at the end of ''Dark Reign'' after being (to the public) the squeaky clean Iron Patriot, when they took his mask off he had Green Goblin paint on underneath... (though in that case, that might have been triggered by [[ComicBook/XMan Nate Grey]], who'd planned to cut the Goblin persona loose from deep within Osborn and show the world what he really was. While Nate lost that round, it looks like he won the war).
** Speaking of Spider-Man villains, [[LizardFolk The Lizard]], aka Curt Connors, also counts.
** As does Mister Negative and his alter ego Martin Lee.
* In ''ComicBook/XMen'', Sauron (no, not [[Literature/TheLordOfTheRings THAT Sauron]]) has this kind of relationship with his alter-ego, Karl Lykos.
* In ''ComicBook/{{Daredevil}}'', Typhoid Mary is the split personality of the otherwise nice and peaceful Mary Walker. She also has the Bloody Mary personality.
* The supervillain Mr. Hyde subverts this trope in a couple of different ways. While the "Hyde" persona is a sadist, the "Jekyll" persona is both an unethical scientist and a perverted DirtyOldMan to boot. Both personas are completely aware of one another, and they happen to get along just fine, although "Hyde" is the dominant personality.
* ComicBook/AlphaFlight's Aurora switched between a free-spirited superhero personality and that of a highly repressed Catholic school teacher.
* ComicBook/TheSentry and The Void.
* The "A Murder in Paradise" StoryArc of ''ComicBook/CableAndDeadpool'' has ComicBook/{{Deadpool}} looking for the murderer of an Osama bin Laden-esque figure who took sanctuary in Cable's island country. Guess who did it and can't remember.

* In ''ComicBook/{{Grendel}}'', what starts out at Hunter Rose's supervillain-identity gradually evolves into a sort of Mr. Hyde alter-ego, which jumps from host to host (or do the "hosts" just share the same psychosis?) over many generations. The Grendel persona best conforms to this trope with the third "host", Brian Li Sung, whose personal journal contrasts the guilt-ridden ponderings of Brian and the emerging rants of the Grendel within.
* ''ComicBook/TheLeagueOfExtraordinaryGentlemen'' includes an aged, monstrous Hyde as a member. Jekyll is now thin and sickly while Hyde is a red-skinned, bulked up giant monster, and it's implied that he was feeding off of Jekyll's energy. Hyde explains it by saying that "without me Jekyll has no drive, and without him I have no restraints."
* Mark Shaw aka Manhunter was constantly tracking a serial killer named Dumas, guess why he could never find him.
* In ''ComicBook/MiniMonsters'' we have Henrietta (The original and good entity) and Miss Hit (The ComicBook/KickAss identity). Her father can also count.

[[folder: Fanfiction]]
* In ''[[FanFic/SovereignGFCOrigins Origins]]'', a ''Franchise/MassEffect''[=/=]''Franchise/StarWars''[[spoiler:[=/=]''[=Borderlands=]''[=/=]''[=Halo=]'']] MassiveMultiplayerCrossover, Sarah develops into a downplayed version of this. She wasn't ever meant to have a personality, but when her controls are removed she manifests a helpful side and a DrunkOnTheDarkSide personality that tries to tempt her back into her old ways.
* In ''Fanfic/GodSaveTheEsteem'', this trope gradually comes into play. At first, Stacy Rowe, a [[ShrinkingViolet wallflower]] high school student whose [[WithFriendsLikeThese friends]] in the Fashion Club are so exhausting to put up with that Stacy gives hanging out with the local group of punks a try, albeit under disguise. But then she grows lonely and weary of trying to find a boyfriend who lives up to either group's standards, so she creates another identity as a nerd. Where this trope comes in is when she loses her grip on her personalities, and begins switching between them without control, and begins blacking out on what the other personalities did. By the time the fic ends she's up to ''five'' personalities: ExtremeDoormat Fashion Club member, violent and alcohol loving punk, perky and upbeat nerdy girl with a stable relationship, paintball gun wielding vigilante, and British soccer team member. Following the timeline of the fic, she was only in control for a few months before she began switching at random. This doesn't end well for her when she snaps and switches rapidly through the whole roster of personalities at school...
* In ''[[https://www.fanfiction.net/s/9305815/1/The-Merry-Killers The Merry Killers]]'', Shinobu Maehara remains the sweet and friendly girl from [[Manga/LoveHina canon]] unless she's wears red. Then she turns into Red, a PsychoForHire assassin who can scare even the other Hinata Sou residents. Shinobu also uses a mirror lined with red tape to communicate wither her other self.

* ''Film/DrJekyllAndMrHyde1931''
* The 2006 film ''Film/AScannerDarkly'' has the main character hunting down a drug dealer who is in fact himself, having developed split personalities from the drug.
* The Creator/AmicusProductions version, ''Film/IMonster'' followed the original novel quite closely but changed the characters' names in the hope of catching the viewers by surprise.
* [[spoiler:The protagonist and Tyler Durden]] from ''Film/FightClub''.
** [[LampshadeHanging Lampshaded]] by Marla: "You're Dr. Jekyll and Mr. [[JerkAss Jackass]]."
* ''[[GenderBender Dr Jekyll and Ms Hyde]]''.
** Itself a Comedic Remake of the darker ''Dr Jekyll and Sister Hyde''.
* ''Film/MeMyselfAndIrene'' had this with Jim Carrey playing two guys in one- nice cop Charlie and bad cop Hank.
* ''Film/RepoTheGeneticOpera'' has Nathan, doting father by day, [[PsychoForHire Repo Man]] by night.
* [[spoiler: Norman Bates and his mother]] in ''Film/{{Psycho}}''. [[ItWasHisSled Only spoilered because]] Creator/AlfredHitchcock [[GrandfatherClause doesn't want us to spoil the movie for others.]]
* [[spoiler: David Callaway and Charlie]] in ''Film/HideAndSeek''.
* ''Film/TheTwoFacesOfDrJekyll'' has an interesting variation. Dr. Jekyll is hirsute, unkempt, ill-tempered and mannerless; Hyde is clean-shaven, well-dressed, well-mannered, and charming. But Jekyll's still a decent guy, and Hyde is thoroughly depraved and evil.
* [[TokenGoodTeammate Glen]] and [[EvilTwin Glenda]] from ''Film/SeedOfChucky''.
* ''Film/AngelHeart'' (1987) with Mickey Rourke.
* ''Film/BiggerThanLife'' shows a schoolteacher Ed Avery (James Mason) abusing his prescription medication and going from an overworked frustrated schoolteacher and husband to a psychopathic and abusive father, with an authoritarian attitude to teaching children. It's implied in the film, that these attitudes and feelings were within him all along but the drug simply provided an outlet.
* Bergman's 'Persona'. The dynamic between Elisabet and Sister Alma; the strange scenes in which one turns the other's head towards her; the reaction of Mr Vogler to Anna.
* Julius Kelp (Sherman Klump in the remake) and Buddy Love in ''Film/TheNuttyProfessor''.
* ''Jekyll and Hyde... Together Again'' had Mark Blankfield going from humble doctor to drugged out sex crazed swinger.
* In the original ''Film/TotalRecall1990'', Quaid is actually an implanted personality of the villain Hauser. [[OrWasItADream Maybe]].
* In ''Film/CitizenKane'', Charles Foster Kane tells Thatcher early on, "The trouble is, you don't realize that you're talking to two people," referring to himself as both a man of wealth and as a man of the people. One of the main points of the movie is the internal war between those two sides. [[spoiler: It can be argued that both sides lose by the end of the movie.]]
* Nick and Francois in ''Film/YouthInRevolt''.
* ''Film/OtherHalves'' is about an dating app that creates that unleashes the user's "other half," or id.

* ''Literature/TheStrangeCaseOfDrJekyllAndMrHyde'', which is the TropeNamer, gives us the [[UnbuiltTrope unbuilt variant of this dynamic]]. Henry Jekyll is a good man with evil urges who deliberately created Edward Hyde for a selfish purpose and, up until a murder was committed, derived pleasure from his darker self's actions. He began to need more of the potion to ward off Hyde taking control and when recreating the formula proved impossible, he wrote a letter to explain everything before dying. The idea of Jekyll and Hyde being the same individual was originally a TwistEnding; the reason for almost all adaptations removing this aspect is that the twist eventually became well-known.
* [[spoiler:Tyler Durden and the narrator]] in ''Literature/FightClub'', though you [[ItWasHisSled probably know this already]].
* Smeagol and Gollum in ''Literature/TheLordOfTheRings''.
* In Creator/NeilGaiman's ''Literature/AmericanGods'' it is revealed at the end and hinted throughout that the paired Slavic gods Czernobog (which translates to [[EvilCounterpart Black God]]) and Bielebog (White God) are a Jekyll and Hyde.
* In the book version of ''Literature/{{Dexter}}'', the lovable SerialKiller is motivated to kill by a sort of being/other personality, the Dark Passenger.
* In the ''Literature/{{Xanth}}'' book ''Crewel Lye'', [[spoiler: there's a Magician named YinYang who spends a lengthy amount of time pretending to be two different people, Yin and Yang, who were having a competition to see which one should be heir to the current King. It turns out that the competition was about which side of his personality should take over.]]
* Nabokov's ''Literature/{{Lolita}}'' has the whole dynamic between Humbert and Quilty leading to the frankly quite trippy scenes at the end, the chase, and especially the murder.
* Odetta and Detta in ''Franchise/TheDarkTower''.
* In ''Skulduggery Pleasant'', there's [[spoiler: Darquesse for Valkyrie]] and [[spoiler: Lord Vile for Skulduggery.]]
* Jekyll's transformation is inverted and averted by Julian Advent of the ''Literature/{{Nightside}}'' series, who faced the same choice as Jekyll when he discovered a similar formula, but chose to drink the version that brought his ''Good'' side to the fore, making him TheCape instead of this trope.
* ''Literature/EdenGreen'''s needle-humans often develop darker 'backup' personalities in order to deal with the horror-show their bodies have become.
* "A Drug on the Market" by Creator/KimNewman is about what happens when a consortium sells Jekyll's formula commercially. Among the test subjects is a clergyman who becomes a [[GenderBender loose woman]] and an anarchist whose "dark side" runs off to get an office job.

[[folder:Live Action TV]]
* Hal from ''Series/BeingHumanUK'' appears to be this with his vampire side. Strange, seeing as neither Mitchell nor Adam appeared to be this, and Hal has drank blood without going full Hyde. It's implied that this is because of his continuous, long running suppression of his vampire instincts, having lasted about fifty five ''years'' longer than either, as the longest either of them has gone straight is a few months.
* Scorpius's suicidal program inside Crichton's head in ''Series/{{Farscape}}''.
* Brainwashed Geordi used as an assassin on ''Series/StarTrekTheNextGeneration''.
** One episode of ''Series/StarTrekVoyager'' has [[spoiler: the Doctor]] develop a villainous split personality which he is unaware of as a result of [[spoiler: making some unwise adjustments to his programming]].
** ''Series/StarTrekTheOriginalSeries'' with "The Enemy Within", where a transporter malfunction splits Kirk's good and evil sides.
* ''{{Series/Jekyll}}'' plays around with the dichotomy. For the first half of the series Jackman ruins his life trying to minimize the damage Hyde could cause, particularly to his own family. Although Hyde is meant to be the most intelligent creature on the planet, his immature mind and Jackman's own substantial intelligence and careful planning allow Jackman to keep a tight hold on Hyde's actions.
* Niki and Jessica from ''[[{{Series.Heroes}} Heroes]]''.
* Season 6 of Dexter has [[spoiler: Travis and Professor Gellar]] turning out to be just one person, they even try to Sixth Sense the twist for nine episodes. It was painfully obvious.
* ''Series/BuffyTheVampireSlayer''. [[spoiler:The BigBad of Season 5 is Glory, a female PhysicalGod imprisoned within the body of Ben, a male human. Although Glory is the more powerful personality, Ben is still able to hamper her to some degree. In the season finale, the distinction between them starts to break down, with Glory beginning to feel genuine human emotions (like sympathy, guilt, and fear) and Ben becoming more callous and self-serving (like being willing to cooperate with Glory's plan in order to survive himself). Eventually they are able to switch back and forth rapid enough to actually talk to each other]]
** More obvious, Angel and Angelus from ''Series/BuffyTheVampireSlayer'' and ''Series/{{Angel}}''. Though at different times in both series that varies between Jekyll & Hyde and EnemyWithin. It all depends on whether Angel simply becomes evil when he loses his soul (as his Series/{{Buffy|the Vampire Slayer}} appearances and Series/{{Angel}}'s fifth season implied) or if losing his soul replaces Angel with the demon soul of Angelus (as it seemed to be in Series/{{Angel}}'s fourth season).
*** Except that Angel losing his soul always leads to the demon Angelus taking over, because Angelus is always there. Otherwise Angel would, at least, not be able to vamp out, and probably keel over dead, being a corpse, without the demon animating him. For proof, see the season 2 finale of Angel. When he tries to vamp out on Pylea, [[spoiler:the demon takes over completely and is a mindless, inhuman monster]]. Angelus, particularly according to that example, is a blend of the demon's personality and sadism with Angel's memories and brain (but not his soul). When Angel loses his soul, it's gone, and all that's left is Angelus. ''All'' of those incidents where he's evil ''are'' Angelus.
** There's also the Series Three episode Beauty and the Beasts, which features a high school student drinking a chemical potion that turn him into a monster who attacks anyone who gets too close to his girlfriend.
* ''Julia Jekyll and Harriet Hyde'' had the main character Julia Jekyll turn into a hairy monster called Harriet Hyde uncontrollably.
* A show called ''Series/MyOwnWorstEnemy'' features a man leading a double life. His normal side is Henry and his alternate ego (that he doesn't know about) is the spy Edward, which is most likely an allusion to the original Dr. Henry Jekyll and Edward Hyde. Reverses the usual Jekyll/Hyde dynamic in that Edward is the original personality; Henry is a construct. While Edward is the edgier of the two personalities, he's not actually evil.
* ''Series/AceLightning'' has Random Virus, who has two personalities, good and evil, signified by his cyborg eye being green or red, respectively. He doesn't seem to have much control over whether he's good or evil, although Ace managed to turn him good temporarily by reminding him that he was a Lightning Knight, and therefore a 'good guy'.
* Playing this trope painfully straight is Darkstrike from ''Series/BirdsOfPrey'': he's a vigilante hunting after the Creeper, the SerialKiller who killed his girlfriend.
* ''Series/WhereInTimeIsCarmenSandiego'' had a girl named Jacqueline Hyde, who jumped from sweet, innocent schoolgirl to raving, snarling harpy at the drop of a hat.
* [[Series/{{Smallville}} Davis Bloome]]/Doomsday.
** Before that, when Clark tried to explain himself to Chloe about not being himself lately (Lionel Luthor had swapped bodies with him), she stated that people sometimes act as Jekyll and then as Hyde but are the same after all.
* Adam Worth from ''Series/{{Sanctuary}}'' is said to be the in-universe explanation for the novel. Neither personality is particularly stronger, but unlike most examples, both sides work in tandem.
* ''Series/{{Supernatural}}'': Kind-and-gentle human Sammy, arrogant-and-violent demonic Sammy. And then there is soulless robo Sammy...
* ''Series/DoctorWho'':
** Used with all the homages to the Franchise/UniversalHorror version of the story with Sorenson in "Planet of Evil", whose addiction to antimatter repeatedly transforms him into a monster.
** Done rather well with [[spoiler: Professor Yana]] and the Master.
** [[spoiler: The Doctor and the Dream Lord]]
** It happens again later in the episode "Nightmare in Silver" with [[spoiler:The Eleventh Doctor]]/Mr. Clever
* Mesogog and Anton Mercer from ''Series/PowerRangersDinoThunder''. Eventually Mesogog splits himself off from Mercer because he gets fed up with sharing. It frees the Rangers to not hold back against him, but he becomes even more effective due to being able to act more often and not just when he surfaces.
** A Similar example are the villains [[TheChessmaster Heckyl]] and [[TheBrute Snide]] from ''Series/PowerRangersDinoCharge''. Subverted with Heckyl being just as evil as Snide but played straight when they are split apart.
* ''Series/TheVampireDiaries'': Stefan Salvatore. He has one side of his personality which is kind, caring, empathetic and compassionate and heroic ("Jekyll", Hero!Stefan) and another side of his personality which is sociopathic, crazy, addictive, cold and ruthless ("Hyde", Ripper!Stefan)
** Alaric Saltzman is a better example. Normally a good-hearted vampire hunter, he develops a serial killer Hyde persona from dying too often.
* 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 and then reverts back at 8:25 am the following morning. 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. [[spoiler: [[SubvertedTrope Subverted]] in the series finale when it was [[TheReveal revealed]] that the benevolent personality was in fact the actual alter while the malevolent one was the original]].
* On ''Series/TheBigBangTheory'', after Penny wakes up with Raj, she refers to herself as Dr. Jekyll and Miss Whore.
* In ''Series/TheDukesOfHazzard'', Luke inadvertently ingests a mind-altering serum. At first he's just snarky and testy to his cousins, but soon becomes despicably evil, terrorizing Hazzard, robbing the bank, disrespecting Uncle Jesse, and even [[RapeIsASpecialKindOfEvil becoming a masher]].
* ''Series/JekyllAndHyde2015'' has Robert Jekyll, grandson of the infamous Dr. Jekyll, and his alternate personality, Hyde. In this Hyde emerges when Jekyll ''doesn't'' take certain drugs.
* In the ''Series/MurdochMysteries'' episode "Excitable Chap", a mysterious Lurker begins not-exactly-terrorising ladies [[spoiler: at the same time as James Pendrick is developing his new brain-enhancement drug. It inevitably turns out that state of unconsciousness he enters after his period of frenzied work is actually him acting out his subconscious desires as the Lurker. When the Lurker seemingly kills someone, Julia points out that if Pendrick isn't a natural killer, his Lurker wouldn't have murder in him either. It turns out someone else has been taking the drug.]]

* "Sacrifice" by Music/{{Disturbed}} is about this trope, along with themes of "My other side is going to hurt you".
* "Mz. Hyde" by Music/{{Halestorm}} is pretty much ExactlyWhatItSaysOnTheTin, and manages to almost fetishize the duality.
* "Jekyll and Hyde" by Music/FiveFingerDeathPunch is, unsurprisingly, about this trope. "Ohweeohweeoh, there's a demon inside! Ohweeohweeoh, just like Jekyll and Hyde!"
* "Dr. Heckle and Mr. Jive" by Music/MenAtWork. Almost a straight-forward summation of the plot of ''Film/TheNuttyProfessor''.
* A variation can be heard in "Battle of Someone" by Music/BluesTraveler. The first verse starts, "Well I love no one," and is generally cynical and embittered. The second verse starts, "Well I love everyone," and is idealistic and hopeful. The final verse contains the line "The preceding verses are the halves of my soul," and describes how the singer recognizes [[SlidingScaleOfIdealismVsCynicism the battle within him between the darker and lighter sides of his being.]]
* The first 5 Albums of ''ASP'' tell the story of the Black Butterfly, a vampire-like entity, which sometimes seems to inhabit the body of the protagonist. For example, in the song ''Lykanthropie (Es tobt ein Krieg in mir)'', it's compared to werewolves, with the protagonist not remembering what he did while under the creatures influence.
** Also, in promotional shots, both the protagonist and the Black Butterfly are represented by the bands lead singer Alexander Spreng.
* Played with in "Bubba Hyde" by Diamond Rio. The song is about an ordinary guy named Barney Jekyll, a grocery store employee and volunteer firefighter who seems like an unhip ordinary man, except on Friday nights, when he dons a leather jacket and zebra boots, and becomes the party animal "Bubba Hyde".

[[folder:Tabletop Games]]
* In ''TabletopGame/{{Pathfinder}}'', the Alchemist class can create a mutagenic potion that changes his/her personality and appearance, making the character more physically powerful at the expense of their mental abilities. The Master Chymist PrestigeClass takes this a step further, allowing the alchemist to create a unique infusion that, when taken, changes the character's personality and CharacterAlignment and possibly gives them a monstrous appearance; the two personas have separate minds and may work against each other. That said, the SplitPersonality doesn't have to be evil, just a different alignment; a LawfulGood chymist could have a ChaoticGood alter ego, for instance.
* ''TabletopGame/MagicTheGathering'', in its Gothic horror-themed ''Innistrad'' expansion, introduced [[http://gatherer.wizards.com/Pages/Card/Details.aspx?multiverseid=221209 "Civilized Scholar"]], a double-faced card that transforms into "Homicidal Brute". He was actually named "Jekyll and Hyde" as a placeholder in the early designs for the set.
* The quevari, a human subspecies from the TabletopGame/{{Ravenloft}} setting, live as benign vegetarian pacifists by day, but are bloodthirsty killers by night. The darklord of Nova Vaasa, Sir Tristan Hiregaard, struggles against his crime-lord alter ego Malken.
* Every character in ''TabletopGame/KindredOfTheEast'': the soul of an eastern vampire is divided into the higher Hun and the lower P'o. It is as troublesome as it sounds, but the P'o is indispensible. It serves as the SuperpoweredEvilSide, providing some essential combat powers (indeed, a vampire couldn't even grow fangs without it) and is responsible for him being undead in the first place.
* Kindred of the East draws on ''TabletopGame/WraithTheOblivion'': in death, the dark side of the living personality, the Shadow, becomes independent, developing its own personality, and can at times gain enough strength to assume control over the wraith. The inverse applies to Spectres, for whom the Shadow is the dominant personality; their light side, the Psyche, remains independent and can at times become strong enough to take control.
* A variant is possible in ''TabletopGame/{{Aberrant}}''. Novas can accumulate physical and/or psychological mutations from various sources (most of which give you power at this cost), and can gain the ability to suppress their superpowered side, including these mutations. Of course, there's no reason that this SuperpoweredAlterEgo has to be ''evil''; it's just as likely to be heroic or villainous as is a "normal" person.

* In the 1933 Broadway musical ''Pardon My English'', a British UpperClassTwit named Michael Bramleigh is unconscious of also being a notorious jewel thief called Golo. A TapOnTheHead causes him to switch between the two identities and their respective love interests.

* Jackson Jekyll and Holt Hyde from ''Franchise/MonsterHigh''. Unsurprisingly.
** Somewhat subverted in that neither of them are evil. Jackson is a rather sweet, quiet, studious boy, whereas his alter ego is louder and more boisterous but still has a good heart. Granted, Holt Hyde is a [[CuteMonsterBoy monster]], but considering the setting that is a compliment.


[[folder:Video Games]]
* Marcus Kane (Roadkill) and Needles Kane (Sweet Tooth) of the ''VideoGame/TwistedMetal'' series.
* Daniel and [[spoiler:Leo]] in ''VideoGame/{{Manhunt}} 2''.
* Emil from ''VideoGame/TalesOfSymphoniaDawnOfTheNewWorld'' has two personalities. First, there is his normal, timid, self-effacing personality. Then there's his "Ratatosk Mode," which is significantly more aggressive, to say the least.
* [[spoiler: Pat and his evil other-self Rey]] in the first ''VideoGame/MegaManStarForce''.
* ''VideoGame/{{Xenogears}}'' - [[spoiler: Fei, the player's character, and Id, the mysterious super-powerful lone villain.]]
* In ''VideoGame/SummonNight Swordcraft Story 2'', one of your Guardian Beasts is a trashtalking demon who claims to have been possessed by her angelic sweet side. Subverted in the matter that the demon is the leading personality, with the angel being the hidden "Hyde".
* Kind of easy to miss, but ''VideoGame/QuestForGloryV'' had [[spoiler:Praetorius and Mobius. While Praetorius is nicer than Mobius ([[JerkAss which isn't all that hard]]), he's still completely okay with poisoning wizards [[ForScience in order to prove science superior]]. The character does change form when he's finally called out on this, but the graphics make it hard to tell, meaning the dialog is the only discernible indicator.]]
* In the ''VideoGame/{{Neptunia}}'' series, [=CPUs=] are a mild example. While there's only one consciousness and they retain all their memories, goals, etc. during the voluntary transformation, their normal and [[SuperMode Hard Disk Divinity]] forms can have very different personalities. TheSlacker Neptune's HDD form is a more mature LadyOfWar is one example. Another is Plutia, who goes from a friendly, scatterbrained girl to a [[BastardGirlfriend stone-cold]], [[TheDreaded ally-terrifying]] {{Dominatrix}}.
* In ''VideoGame/BioShockInfinite'' [[spoiler:Booker and Comstock are the same person.]] In the beginning it's more of an Evil Twin situation - they do not actually "merge" like for example [[spoiler:dead Chen Lin and living Chen Lin]]. Metaphorically, though, [[spoiler:Comstock]] is the evil within [[spoiler:Booker - both are single-minded, cynical and have a high capacity for violence. Booker is also willing to commit massive manslaughter and serve blatant lies to reach his goal (which in the beginning of the game is even quite morally corrupt).]] Later on, the metaphor becomes physical reality. Firstly, [[spoiler:when Booker kills Comstock but is forced to take charge of the Hand of the Prophet and use the Songbird to destroy a Vox Populi attack. Temporarily, he is Comstock in both biology and social function.]] Secondly [[spoiler:when he is transferred back in time to actually merge with the earlier version of himself that is set on the path of becoming Comstock. When this past Booker "remembers" his future actions as the Hyde, he chooses to let himself be killed. The hero has, indeed, "caught himself".]]
* It turns out that, in ''TheSuffering'' and its sequel, [[spoiler:whenever Torque transforms into a Malefactor, it's actually his second personality, Blackmore, coming to the forefront.]]
* Doshin, the kind, benevolent, helpful giant, and Jashin, the evil, sadistic, vicious version, in ''VideoGame/DoshinTheGiant''.
* The very uptight Berio in ''VideoGame/DuelSaviorDestiny'' has an exhibitionist kleptomaniac side in Black Papillon that she developed as a way of dealing with stress. While Berio is highly disapproving of how her other side reacts and seems unaware, deep down she knows that it's probably her.
* ''VideoGame/{{Borderlands 2}}'' has Krieg, who is split between the dominant, psychotic personality and a subdued sane personality. The latter tries to ensure that the former only kills "the deserving" and even swears that if the latter ever sheds innocent blood that it'll take over and commit suicide. In response, the psycho personality will even bash himself in the face with his axe to silence the voice.
* In the iOS game ''VideoGame/LaytonBrothersMysteryRoom'', [[spoiler: Alfendi]] is in this predicament thanks to an incident 4 years ago. However, it seems that the [[spoiler: "Hyde"]] is the really personality while his new persona is the [[spoiler: Jekyll]].
* In ''VideoGame/MetalGearAcid'', Solid Snake realises he knows a lot more about the facility than he expected. It's explained to him that he took the alias "Hans Davis" to perform some hideously unethical experiments on psychic children, and through repressing his memory of these events and of all the other terrible things he's done in his life, the ruthless and evil Hans has become an alternate personality into which he occasionally switches or even hallucinates conversing with. [[spoiler: This is eventually revealed to all be the result of psychic {{Gaslighting}}.]]
* ''VideoGame/TheUltimateHauntedHouse'' has Gahan Wilson, the ghost host of the mansion, suffering from a SplitPersonality due to a formula he drank, splitting him into a good and evil side. The good one will give hints and items to the player. The bad one will curse the player, steal items, or summon monsters into the room. Part of the challenge of the game is determining whether Gahan is good or evil at any particular moment, especially considering [[HydePlaysJekyll Evil Gahan will pretend to be Good Gahan]] in order to lure you into a false sense of security.

[[folder:Visual Novels]]
* Angel Starr from ''VisualNovel/PhoenixWrightAceAttorney'', complete with PeekABangs moving from one eye to another depending on whether she's sweet or sour.
* Tohno Shiki from ''VisualNovel/{{Tsukihime}}''; when either his life is in extreme danger or he is confronted with something non-human he loses grip on his consciousness and becomes the [[SuperpoweredEvilSide amoral sociopathic killer]] Nanaya Shiki, who is a ''highly'' skilled assassin. Slightly subverted, though, in that [[spoiler:despite being the main personality, Tohno Shiki is the false, created identity while Nanaya Shiki is the 'original' (yet Nanaya rarely ever appears). Nanaya is the Shiki who would have been, had his clan not been wiped out during his childhood and him hypnotized and brainwashed later on into becoming Tohno Shiki.]]

[[folder:Web Comics]]
* Chastity and Prixen, Martina and Sweater Puppy in ''Webcomic/TheMagnificentMilkmaid''.
* Anna and Susan in ''[[http://Sire.smackjeeves.com Sire]]''. Indeed, they obsess over the original Stevenson work, and are even [[spoiler: descended from Edward Hyde]].
* [[spoiler:It seems that Ples Tibenoch]] of Tessa Stone's ''Webcomic/HannaIsNotABoysName!'' has a Jekyll and Hyde disorder of sorts.
* When [[spoiler:Gamzee Makara]] of ''Webcomic/{{Homestuck}}'' is stoned, he's one of the sweetest, most goofy LoveFreak characters in the whole thing. [[BewareTheSillyOnes But]] [[AxCrazy when]] [[MonsterClown he]] [[OmnicidalManiac gets]] [[NoMedicationForMe sober...]]
** [[spoiler:Calliope and her "brother"]] share a body, and switch places whenever one goes to sleep or hears the other's name. [[spoiler:Calliope]] is one of the sweetest and most helpful people the [[spoiler: Post-Scratch]] Kids have. Her brother, [[AxCrazy on]] [[JerkAss the]] [[BloodKnight other]] [[LaughingMad hand]]... This is actually ''normal'' [[BizarreAlienBiology for their species.]]
* ''Webcomic/BramAndVlad'' has Henry E. Jekyll and his counterpart, Jack Hyde. You can tell them apart because Hyde is a violent thug with red eyes, sharp teeth, sharp nails and he [[ArsonMurderAndJaywalking supports Argentina during the World Cup]].
* Henry Jekyll and Edward Hyde again in ''Webcomic/TheGlassScientists''. Jekyll is a polite socialite hiding a high school's worth of insecurities while Hyde is ever-smiling self-described "creature of the night".
* In the retelling of the classic story, ''Webcomic/MKsTheStrangeCaseOfDrJekyllAndMrHyde''. Jekyll is a law abiding sweetheart to a fault of the high society who constantly fears confrontation especially with the Carews making him prone to getting walked all over. Hyde is a cocky vagabond of the lower class who just takes what he wants even if it means committing theft and he is not above being a ruffian or openly defying the Carews. Unlike most depictions though, this one depicts Hyde as not being evil deep down and just wild and selfish.
* ''Webcomic/TheSearchForHenryJekyll'' has Jekyll and Hyde, but also Dr. Lanyon, who gained a split personality when Hyde injected him with the same formula used to make him.

[[folder:Web Original]]
* This is how [[WebVideo/TheSpoonyExperiment Spoony]] and [[spoiler: [[MadScientist Dr. Insano]]]] are portrayed in the Website/ThatGuyWithTheGlasses anniversary special ''WebVideo/{{Kickassia}}''. (This is subject to NegativeContinuity.)
** NegativeContinuity indeed. [[spoiler: ''WebVideo/ToBoldlyFlee'' had retconned this into an anomaly caused by the PlotHole, in 'reality', Spoony and Insano are indeed two separate people.]]
* Flippy from ''WebAnimation/HappyTreeFriends''. He's usually sociable, sweet and friendly most of the time, but whenever he sees or hears something related to his war past, he goes into his evil state and brutally murders his friends, believing they are enemy soldiers.
* [[WebVideo/TheNecroCritic Necro Critic's]] sidekick, Devil Critic, is introduced in one of these plots. However, as a subversion, he turns out to just be Necro's brother filling in for him while he's [[ItMakesSenseInContext in an energy drink induced coma.]]
* [[WebAnimation/AlfredsPlayhouse Alfred]] himself is a depressed, naïve dog while his alter ego Dictator Pickles threatens to enslave the world's populace. Though Lucifer, his other alter ego, appears closer to the Hyde archetype: appearing to want nothing other than to destroy kill, and rape.
* ''WebVideo/GemmaAndTheBear'' is a non-villainous example PlayedForLaughs. Gemma is a nerdy, neurotic white woman who turns into a cheerful, extroverted, gay black man named Bear when she falls asleep. They can't interact directly but are aware of each other, with Bear fancying himself Gemma's [[GuardianEntity protector]]. His attempts to be helpful mostly drive her nuts, and, in the first season finale [[spoiler:bring the FBI to her doorstep]].
* VenturianTale : This or [[DemonicPossession demonic possession]] appears to be the case with [[OccultDetective Johnny Ghost]] and [[KnifeNut Jimmy]] [[SerialKiller Casket]].

[[folder:Western Animation]]
* In the ''Franchise/{{Transformers}}'' universe, the Autobot Punch adopted a Decepticon personality as Counter-Punch, so as to play a double agent. He has lost some sense of self-identity because the Counter-Punch personality takes over, leaving him with a sense that he's missed out on the past hour or so.
** It also happened in ''WesternAnimation/BeastMachines'', with Savage and Noble. Savage is a blind, insane, vicious dragon, while Noble is an intelligent and cunning [[{{Wolfman}} wolfbot]]. [[spoiler: Subverted, in that they're Megatron, playing their sympathies to get into position.]]
* Several times in ''WesternAnimation/JackieChanAdventures'' is Jackie split into a good and bad side, usually via the Tiger talisman. These two sides are the same person and represent the balance in all humans of a good and bad side. Ironically, this occurs in one episode in which Jade is performing in a play about Jekyll and Hyde.
** It's not really "good" and "bad" so much as "moral pacifist" and "amoral badass":
-->'''Jade''' (pointing to amoral Jackie): You're evil! EVIL!
-->'''Uncle''': Not evil. Only misguided.
* ''WesternAnimation/SpiderManTheAnimatedSeries'' - Norman Osborn and the Goblin; unlike most depictions, this version of Osborn was a decent guy (or at least trying to be one), while the Goblin was as homicidal as ever.
* Morph from the ''WesternAnimation/XMen'' animated series, after coming BackFromTheDead, often wavered back and forth between his normal, "Jekyll" self and a semi-undead "Mr. Hyde" alter-ego who blamed the X-Men for leaving him behind on a failed mission. It turned out he was [[BrainwashedAndCrazy mind-controlled]] by the season's BigBad, but the effects didn't leave him for a good while afterward.
** At one point, he even hides out with a theater troop, where he performs "Jekyll and Hyde", using his [[VoluntaryShapeshifting shapeshifting]] powers to play both roles.
* The 1950 [[WesternAnimation/ClassicDisneyShorts Goofy cartoon]] "Motormania" features Goofy as the mild-mannered, friendly Mr. Walker. However, whenever Mr. Walker gets into his car, he becomes the ill-tempered, violent, and [[DrivesLikeCrazy reckless Mr. Wheeler.]]
* The second SuperheroEpisode of ''WesternAnimation/JimmyTwoShoes'' featured a large, green monster that constantly attacked Lucius. It was eventually revealed to be Samy, who was constantly transforming thanks to one of [[MadScientist Heloise's]] potions.
* ''WesternAnimation/MaryShelleysFrankenhole'' has ''the'' Jekyll and Hyde, whose serum causes Creator/JohnBelushi to turn into [[Creator/JamesBelushi Jim Belushi]]. Victor [[DeconstructedTrope also ridicules him]] for being his own monster.
* ''WesternAnimation/{{Arthur}}'': "Jekyll, Jekyll, Hyde, Jekyll, Hyde, Hyde, Jekyll! "Jekyll, Jekyll, Hyde, Jekyll, HYDE!!!"
* The ''WesternAnimation/{{Beetlejuice}}'' episode "Dr. Beetle And Mr. Juice" has B.J. creating a perfume that has a weird effect--it turns whoever applies it into their opposite personae. When it accidentally hits Lydia, she turns from being sweet and introverted into an obnoxious prank-playing biker.
** There was another episode where Beetlejuice briefly visited a doctor in the Neitherworld whose Jekyll self was patient in getting Beetlejuice to cooperate, but would turn into Hyde when BJ started to get on his nerves.
* ''WesternAnimation/TheRobonicStooges'': "Dr. Jekyll And Hide Curly" has Dr. Jekyll's formula creating a Mr. Hyde on the ''back'' of his head only. He captures the Stooges and creates Hydes on the back of their heads that makes them imprison themselves.
* ''WesternAnimation/BatmanTheAnimatedSeries'' added another variation to this in Two-Face in the final season - he'd established a ''third'' personality called "The Judge", who targeted Gotham's costumed villains, including Two-Face himself, who would GoMadFromTheRevelation.
* It must have been Creator/FrizFreleng's favorite book, because he did three or four cartoons on the theme for Warner Bros., and a couple more at Depatie-Freleng Enterprises.
** Specifically - ''WesternAnimation/LooneyTunes'' - Friz Freleng seemed fond of this plot. He used it in "Hyde and Hare" (with Bugs Bunny), "Dr. Jerkyl's Hide" (with Sylvester), and "Hyde and Go Tweet" (Sylvester and Tweety). "The Inspector" episode "Sicque! Sicque! Sicque!" where Sgt. Deux-Deux drinks the classic potion and becomes a monster. In "Pink Lightening" the same happens to The Pink Panther's car and "Watch The Birdie" is pretty much a remake of "Hyde and Go Tweet" with "The Dogfather" characters instead.
* ''WesternAnimation/YogisSpaceRace'': Captain Good and Phantom Phink. A Space Race biography even described Phantom Phink as Jekyll's descendant. [[IdenticalGrandson With "Dr. Jekyll" looking like "Captain Good" and "Mr. Hyde" looking like "Phantom Phink"]].
* ''WesternAnimation/ThePerilsOfPenelopePitstop'': The Hooded Claw once rented a house from Jekyll and Hyde as part of a plan to capture Penelope. After realizing there was no tea there, he improvised with some random ingredients. He planned to have the Bully Brothers capture Penelope while he distracted the Ant Hill Mob with the tea. However, the tea turned them into seven Mr. Hydes and they captured Penelope. To get their SentientVehicle to cooperate, they gave it some of the "tea" and it also became a Mr. Hyde.
* ''WesternAnimation/AtomicBetty'': Minimus' two personalities. The book was even mentioned in the episode where he got stuck on "Hyde" mode.
* ''WesternAnimation/CountDuckula'' - episode "Doctor Goosewing and Mr. Duck". Von Goosewing invents a potion that reverses everyone's personality. He and Duckula become "wicious wampires", Igor becomes happy and loving and Nanny becomes a brainbox.
* The ''WesternAnimation/DextersLaboratory'' episode "Monstrosi-Dee Dee" has Dee Dee drinking an experimental apple and repeatedly turning into a monster and back. The episode is a ShoutOut to Friz Freleng's cartoons mentioned above.
* ''WesternAnimation/ScoobyDooWhereAreYou'': "Nowhere To Hyde" (season 2, episode 1) mixes this with the standard ScoobyDooHoax. A diamond necklace is stolen by a figure people see is the Ghost of Hyde. The gang (after circumstances from confronting Hyde) follow him to a house in the woods where they meet Dr. Jekyll, who says he's the ghost of Hyde after attempting to mix and test a vitamin formula. The standard investigations and chases ensue and after Hyde is captured, it turns out the Hyde ''was'' Dr. Jekyll in a mask who tried to frame his housekeeper for the crime.
* The ''WesternAnimation/StaticShock'' episode "Tantrum" had Virgil Hawkins/Static's classmate Thomas Kim transform into a purple behemoth whenever he got angry. Static even compares the transformation to Jekyll and Hyde.
* The eponymous character of ''WesternAnimation/{{Kaeloo}}'', who is normally a [[NiceGirl cute, gentle]] frog, transforms into a [[HulkingOut huge, buffed]], {{Sadistic}} toad whenever she gets angry. Some episodes imply that she knows what she's doing, but others imply that she has no control over this.
-->'''Kaeloo:''' What did I do this time?

[[folder:Real Life]]
* According to Colin Willson's ''History of Murder'', the Thugee cult of India were sort of a TruthInTelevision example of this achieved through brainwashing, as they would lead normal lives most of the time, but then commit mass murder when seized by bloodlust. Wilson includes comments from Thugs to the effect that while generally they treated their killings as committed as within a dream, many felt that this murderous life was the real one rather than their respectable life.
* Musth, a hormonal surge experienced periodically by adult male elephants, can turn even the friendliest of pachyderms into a temperamental, violent threat.
* Locusts live as timid, solitary grasshoppers until their population gets too concentrated, at which point their hormonal levels shift and they begin swarming, migrating ''en masse'' and devouring every bit of vegetation in sight.
* The infamous Zodiac killer claimed this in one of his letters. He said that he would "lose all control" to his Zodiac persona soon, and set up a bomb to blow up children. However, this may have been just a trick to humiliate the police once again.

* Wiki/TVTropes: SugarWiki and DarthWiki.