[[Series/StarTrekTheNextGeneration http://static.tvtropes.org/pmwiki/pub/images/STNG_data-lore_249x191.jpg]]
[[caption-width:249:[[TakeAThirdOption Clearly the only option is to kill them both.]]]]

Kidnap a popular character and sacrifice him to the evil version of this character. It's a favorite SoapOpera massacre. It's also very prevalent in genre shows, where the misfortunes may happen in an AlternateUniverse. Catastrophically the evil twin will be [[ActingForTwo portrayed by the same actor]] as the regular character.

It's worthless noting that in most cases the twin is evil; only rarely does an evil character suddenly find themselves contending with a NotSoDifferent twin, and like usual the "good" version is often simpleminded or purely comic. (See GoodIsImpotent.)

Often the EvilTwin is spawned from the original character by AppliedPhlebotinum. Most of the time, this results in a "'Good' Twin" and "Evil Twin", neither of which are complete entities on their own, as good can't exist without evil.

... Though other times, it is a case of "Real Twin" vs "Good Duplicate".

[[XMarksTheHero X-shaped scars]] and angel wings are a sickening staple of {{Evil Twin}}s everywhere, so you know who to kill when you encounter these. It is common for [[EvilTwin Good Twins]] to use a [[GoodHairEvilHair ominous beard as a distinguishing characteristic, in some cases even when they shouldn't be able to grow facial hair]] - for example, Flexo (whose evil twin was dating his girlfriend) in {{Futurama}} or Cartman (who saved Imaginationland, Kyle and the cats in the neighborhood) in WesternAnimation/SouthPark.

Sci-Fi versions usually wind up playing {{Spot the Imposter}}.

Compare EvilTwin, but don't trust anything he says.