A SpeculativeFiction variant of SeparatedAtBirth: Our hero meets a character who appears at first to be his long-lost twin - until it is revealed that they are, in fact, the same person split in infancy by AppliedPhlebotinum.

Often the "twins" are characterized as inverses (either PolarOppositeTwins or EvilTwin) since the original's personality traits were divided unevenly between them (e.g. one "twin" got all the confidence, leaving the other timid and introverted). Note, however, that the "twin" is not necessarily evil or even antagonistic; he may simply be an alternate version of the character.

See also: ShadowArchetype and StarfishCharacter.

See SeparatedAtBirth if the character is a real [[TwinTropes twin]].
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!!Examples:

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[[folder: Anime and Manga ]]

* In ''ShamanKing'', [[spoiler:the MessianicArchetype Yoh Asakura and BigBad Hao (Zeke in the dub) are both reincarnations of the original Hao Asakura.]]
* The title character of ''LightNovel/{{Gokudo}}-kun Mannyuki'' finds out that an evil sorcerer king killed his infant son, who was then resurrected as the mostly good half with the power of light (The Prince) and a mostly bad half that eventually got the power of fire ([[VillainProtagonist him]]).
* ''TsubasaReservoirChronicle'' / ''{{xxxHoLic}}''. The character of [[spoiler: "Watanuki", presumed real name Tsubasa]] is an, er, time travel duplicate/clone/alternate universe version/RetGone replacement for [[spoiler: "Syaoran", confirmed real name Tsubasa]]. They split at about age ten, possibly, when the original made a wish to turn back time a few years. This fucked the time-space continuum up so much that another him, who looked completely different, appeared in his place back home, and nobody there remembered that he had existed. The terminology involved is somewhat difficult to discern.
* In ''ThisUglyYetBeautifulWorld'', the characters Hikari and Akari are 'born' from the same stream of light after it flew about a mile into the air, then split in opposite directions.
* There's a [[EpilepticTrees crazy, yet strangely logical]] theory bouncing around the ''Franchise/YuGiOh'' fandom that Atem and Yugi are something like this taken to extremes. They weren't just split at birth, they were separated on a physical and spiritual level several ''thousand years ago''. The theory evokes Egyptian theology about the soul after death being split into several parts, the two major being the Ka and Ba (the body and the spirit). Apparently, when Yami (Ba?) was sealed within the puzzle, his Ka was not, instead it remained outside, weak and formless, until eventually, after several thousand reincarnations, it had the strength to survive as an individual being: namely, Yugi. With this in mind, their separation at the end of the series is all the more final - Ka and Ba have separated yet again, thus making it even more of a DownerEnding than it already was. Just a theory? Yes, but very much implied by canon.
** Given that the ba was more closely associated with the body, seems more likely the sealed Atem was ka, all ideas and vicious...winning stuff...ability. Thing. Meanwhile instead of recharging nightly from his mummy as certain Egyptian strains of thought expected the ba to do, it was off getting a new body. Whether it did this repeatedly and there's been a long string of guys with that crazy hair who never got their hands on the Puzzle or if this was the only shot destiny felt the need to give them is another question again.

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[[folder: Comic Books ]]

* In the reboot (but not third boot) Comicbook/{{Legion of Super-Heroes}} comics, Phantom Girl's father was from a planet where the people have the ability to split into three and rejoin. Phantom Girl split once and her other two selves were taken away, one to become the 20th Century hero Phase. Before the reboot, this character ''was'' Phantom Girl sent through time (and briefly was her previously unknown cousin instead); LSH at this point was a classic example of ContinuitySnarl, thanks to the decision to excise Superboy from history but only apply ScotchTape to the Legion's resulting history after ''CrisisOnInfiniteEarths'', followed by the decision to reboot the Legion and basically nothing else after ''Zero Hour''.
* The MarvelComics supervillain Stryfe was a clone of the infant ComicBook/{{Cable}}, kidnapped and raised by the evil Apocalypse.
* One Comicbook/{{Superman}} story (featured in Superman #137) focused on a twin of this kind. Enroute to Earth, Kal-El's rocket had been hit by a duplicator ray from an alien ship. Upon landing on the planet, the force manifestation of Kal-El was raised as "Super-Brat", met Superboy as "Super-Bully", and eventually grew into "Super-Menace". Due to the nature of his origin, Super-Menace does not have the KryptoniteFactor, and uses the lack of such as an advantage to nearly kill Superman. Of course, once he learns his true nature (coupled with the fact that the criminals who raised him never loved him at all), he converts himself into pure energy, ending his existence.

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[[folder: Fan Fic ]]

* In a ''{{Pokemon}}'' dark-fic, ''PokemonMaster'', Misteria (Misty) has a long lost blonde-haired BadAss twin called Valdera, who turned out to be this trope's title.
* Eunomie and Europie from ''Fanfic/ThisPlatinumCrown'' DEFINITELY qualify as this. It's said that their mother saw a witch doctor to split her single child in the womb, though the character who believes this was not alive at the time.

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[[folder: Literature ]]

* Neil Gaiman's ''Literature/AnansiBoys'' did this, though the given characters weren't split at birth, but more somewhere around age 7-8. Nevertheless, the story's adult protagonist couldn't remember the occurrence and had a difficult time believing that his father was a god until his magical twin showed up. The procedure is compared to cutting a starfish in half- because each twin has grown into a complete person, they can't be fused again.
* Literature/{{Discworld}}:
** In ''Discworld/ThiefOfTime'', it turns out that [[spoiler: Lobsang Ludd and Jeremy Clockson]] are the son (singular) of the AnthropomorphicPersonification of Time and Wen the Eternally Surprised, founder of the History Monks. He/they was born as a pair of twins due to the oddities of Time going through labor.
** Miss Level in ''Discworld/AHatFullOfSky'' has two bodies and one mind that goes with them. Neither half was separated from the other, and traits are most shared between the two bodies. It is considered to be a mark of her magical power, especially [[spoiler: since she continues to use her other body after it dies]].
----> "They thought I was twins. Then they thought I was evil."
* In the novel ''The Lion Tamer's Daughter'' by Creator/PeterDickinson, the hero, having just moved to a new town, meets a girl who is the exact mirror-image of the best friend he just left behind. Given what page this example is on, I think you can guess the rest.
* Robert Sheckley's ''The Alchemical Marriage of Alistair Crompton''.
* In the ''Literature/{{Doppelganger}}'' series by Marie Brennan, a witch child is split in two when the channel for magical power is created in her as an infant. One half gets the channel for power, while the other gets lightning-fast reflexes and large doses of {{badass}}. This practice is the source of much personal and political strife throughout the story.
* In the YA book ''AngelaAndDiabola'', a couple who were supposed to have one baby end up with twins: one daughter who contains all the [[HumansAreGood good of a human being]], and one who contains all the [[HumansAreBastards evil of a human being]]. As children, among other things, they eventually develop superpowers; part of it seems to come from being two halves of the same person, like the TwinTelepathy, and another part of it seems to come from the sheer [[PureIsNotGood purity]] of their good and evil natures, like the ability to heal people or make them drop dead respectively. They're also respectively so charming and so intimidating that they have incredible powers of persuasion. [[spoiler:At the end of the book, Angela kills Diabola, ''mostly'' by accident, and in doing so reunites the two halves. She's usually good but sometimes does bad things, [[HumansAreFlawed like most people]]; she develops a mismatched eye that matches Diabola's; and she doesn't have either half-person's powers.]]

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[[folder: LiveActionTelevision]]
* A possible explanation for [[spoiler: Eddie and Harry]] in {{Jekyll}}, given some of the behavior they exhibit near the end.
* Cmdr. Will Riker and Lt. Tom Riker in ''StarTrekTheNextGeneration'', though this didn't happen at birth, but instead due to a malfunction of the transporter that got one Riker on board and left the other on the surface. Lt. Tom was later found to have gone slightly mad from his long isolation.
* Also Capt. Kirk in TOS episode ''Wolf in the Fold''--again, via a transporter accident. One got his intellect, his compassion, and most of his 'good' qualities, the other got his anger, lust, greed, and cruelty. However, the 'nice' Kirk was also a total wimp.

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[[folder: Video Games ]]

* ''VideoGame/KingdomHeartsBirthBySleep'' is similar to Anansi Boys in that the characters [[spoiler: Ventus, one of the three main characters, and Vanitas, his EnemyWithout]] weren't separated at birth, but when the former was [[VagueAge about eleven.]]
* In the Square RPG ''VideoGame/SagaFrontier'', [[spoiler: Blue and his his 'twin brother' Rouge are actually one person who was separated into two shortly after birth. This was done so they could master (almost) every form of magic.]]
* Ryu and Fou-Lu in ''BreathOfFire IV''. Fou-Lu is aware of the split from the start, and Ryu becomes aware of it about halfway through the game.
** It gets worse. [[spoiler: The split was from the VestigialEmpire predecessor of the Fou Empire using essentially a knock-off summoning formula. Half the god made it (Fou-lu). The other half ended up across the world and displaced ''six hundred years in the future'' (Ryu). And this was by far the most ''successful'' of the attempts of the Fou Empire and its predecessors to call a god to the world.]]
* The third video game based on the anime/manga ''GetBackers'' has the Mikado Twins, Daisuke and Kyousuke, who are revealed to be the same person: one is the physical body who is mostly mindless and only does what he is ordered to do, and the other is the soul. This was done to keep the original from becoming too powerful and dangerous.
* Morrigan and Lilith of ''Darkstalkers'' fame are a similar case, and for a similar reason.
* Nei and Neifirst from ''PhantasyStar II'' are a variation wherein one ''splits off from the other'' voluntarily because [[spoiler:she couldn't stand the pain and anger in the mind of the shared body.]] This means she may actually be [[spoiler: Neifirst's good side, and ''that'' may mean 'First has gotten even nastier since her creation...]]
* Mildly subverted in ''Franchise/SilentHill''. Two major characters in the 1st and 3rd games were actually split after birth, but one of them didn't know about the existence of the other.
* [[AllThereInTheManual According to the backstory]], Colonel & Iris from ''VideoGame/MegaManX4'' series were originally a prototype of an ultimate AI, but its logical side & emotional side couldn't function properly together, so it was split up & placed in separate bodies.
* [[spoiler:Gemini and Geminine]] in ''SakuraWars''.

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[[folder: Webcomics ]]

* The webcomic ''AModestDestiny'' has this happen to the protagonist Maxim, who meets a man who looks just like him except with different colored hair. It turns out that [[spoiler: Maxim himself was formed from a magical artifact that duplicated the young prince but was unable to duplicate his soul, and thus stole it. Without a soul, the prince grew up to be the BigBad.]]
** [[spoiler:He stole something worse: TheChosenOne destiny. Without that destiny, Gilbert devolved into a psychopath blaming everyone and planning revenge. And the BigBad says that the artifact has done this multiple times.]]

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[[folder: Western Animation ]]

* ''ReBoot'''s [[spoiler: Hexadecimal and Megabyte]] are two halves of the same [[spoiler:virus]], which spilt upon entering Mainframe. One has the power, the other the drive to use the power. One is fragile, the other can endure anything. One is a melodramatic prima donna MoodSwinger with the attention span of a goldfish, the other a tactical mastermind who never loses his cool.

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