Twin. Doppelgänger, with an umlaut, is the German word for a ghostly double of a living person or more commonly simply a word for someone looking exactly like someone else, i.e. an impostor or double. It means "double (walker)", in the original.

Traditionally, Doppelgängers have strange, supernatural origins, unlike twins which usually have more natural explanations. A MirrorUniverse, Cloning, alien intervention, and magic are all possible sources of a Doppelgänger. For purposes of clarity, this this index includes both mundane and supernatural impersonators of a character.

!!Specific types of doppelgangers include:
* BodySnatcher -- Doppelgangers created by bodily possession.
* CloningBlues -- Clones are one common way of making duplicates.
* CostumeCopycat -- When a hero is impersonated by someone in a nearly identical costume.
* DeadPersonImpersonation -- When one person takes over another's identity.
* DoppelgangerReplacementLoveInterest -- That LoveInterest that just died? S/he has a duplicate in the real world that wants to shack up with you.
* EasyImpersonation -- When a hero is impersonated by someone in a not-even-similar costume.
* EvilCounterpart - A character (not related to the hero) who is very similar, but ForWantOfANail turned evil.
* EvilKnockoff - when a robotic duplicate or clone is made of a hero with the purpose of destroying them.
** MobileSuitHuman -- When the robot duplicate is piloted by a tiny alien.
* EvilTwin -- When a character has an evil sibling or alternate reality duplicate.
* FreakyFridayFlip -- When two people switch bodies, the result is remarkably doppelganger-like.
* IdenticalStranger -- For some reason, the gene sequencing fairy took the day off and you have an unrelated twin.
* JekyllAndHyde -- When the person is their own doppelganger.
* MirrorMatch -- When a character fights themselves in a video game... or a reasonably close match.
* ThePsychoRangers -- An ''entire team'' of doppelgangers to the FiveManBand.
* ReplicantSnatching -- Or when a robot/alien [[NightmareFuel peels off the original's skin and wears it.]]
* ShapeShifting -- Some doppelgangers can do it by shape shifting.

!!Related tropes:
* AntagonistsAssimilate -- Most villainous doppelgangers easily impersonate their target.
* BecomingTheMask -- What happens to many doppelgangers.
* GlamourFailure -- Not all doppelgangers can hide their tells.
* GuiseWillBeGuise -- An impersonator tries to fill in for someone else and HilarityEnsues.
* IdentityImpersonator -- A ploy heroes use to throw off people are snooping their SecretIdentity.
* MirrorUniverse -- Home to many morality opposite versions of a cast.
* PrinceAndPauper -- Two people switch lives.
* SpotTheImposter -- When the friends of the impersonated have to figure out who the spy is.

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