[[quoteright:350:[[Film/TheParentTrap http://static.tvtropes.org/pmwiki/pub/images/f4527c0cc577883d048c0c4f1b9ce901.png]]]]
[[caption-width-right:350:When you meet your [[SeparatedAtBirth lost twin]], the opportunities for pranks are endless. Even when your twin is you.]]

->''"Creator/DavidWarner, you are under arrest by order of Creator/DavidWarner!"''
-->-- '''[[Series/MysteryScienceTheater3000 Crow T. Robot]]''', ''The Quest of the Delta Knights''

The character you know and love walks off set on one side, and a couple of seconds later walks in on the other side, only he's wearing different clothes! And talking funny! And everyone's calling him Cousin Rick, not Fred!

For many a reason both solid and sordid, an actor might find themselves playing more than one role on the same show. It might be a twin brother (or cousin, aunt, etc. -- television has never been fussy on the details). A male character may be put in drag to play his own mother, who [[UncannyFamilyResemblance looks a lot like him]]. More than a few action shows have had a lookalike try to frame the main character. Whatever the reason, the actor is Acting for Two. Sometimes more, depending on the role.

It happens occasionally in other media as well, but when the same actor plays multiple characters on TV or in a film, it usually has a very specific purpose. In theatre, it's just as often an economic use of talent. Often certain role-pairings become traditional, so for example some film versions of ''PeterPan'' still cast the same actor for Hook and Mr Darling - even though they could afford two actors, and the stage tradition only arose because of their lack of scenes together. [[EveryoneIsJesusInPurgatory Maybe because it seems symbolic of... something]].

This tradition goes way way back. Classical Greek drama was usually performed by two or three actors (wearing masks) plus chorus. As a result, you never see more than three principal characters at the same time, in very specific combinations: Hecuba talks to Cassandra and a Greek Herald, then Cassandra goes offstage (and changes masks) and comes back on as Andromache, then Andromache and the Herald go offstage and come back as Helen and Menelaus... To this day "doubling" of roles is common in theatre, especially in NoBudget productions.

This particular little ice cream cone comes in several flavors, depending on the purpose, and varying in utility by medium:

* AndYouWereThere: Like a MirrorUniverse, but with a fun-house mirror (think "Wizard of Oz").
* ButYouWereThereAndYouAndYou: A character tells a story, and the characters are depicted as people the storyteller knows.
* CastAsAMask: An inversion. Different actors play a character's different identities.
* CloningBlues: Well, technically, a clone ''is'' related to you...
* {{Doppelganger}}: An in-story reason for them to be played by the same actor.
* DoppelgangerReplacementLoveInterest: Hooking up with someone identical to your lost love.
* DreamSequence: Not quite the same character, but pretty close.
* GhostInTheMachine: When "the little guy in your head" looks just like you.
* GoodAngelBadAngel: When the angels on your shoulder look just like you.
* IdenticalGrandson: A character's descendants are played by the same actor.
* IdenticalStranger: A new character arrives who looks just like an existing character.
** CriminalDoppelganger: That new character also happens to be a wanted by the police.
** PrinceAndPauper: IdenticalStranger + SwappedRoles + PrincessForADay + FishOutOfWater.
* InexplicablyIdenticalIndividuals: When multiple, nominally unrelated characters are all identical.
* LatexPerfection: Different character, same actor, because character has a perfect disguise.
* LoadsAndLoadsOfCharacters: If you don't have loads and loads of actors to go with them, you get this problem.
** LoadsAndLoadsOfRoles: Very common in theatrical productions, wherein everyone has to be there every single night anyway. In some plays, usually of the more comedic variety, you may get people Acting For Two Dozen. ''Theatre/The39Steps'' for example.
* LostInCharacter: A character who is an actor gets so into character they basically become a new character.
* MirrorUniverse: When everybody has their counterpart, you can have twice as many characters per actor.
* PlayingTheirOwnTwin: Characters who are [[AlwaysIdenticalTwins identical twins]] (or triplets, quadruplets, etc.). Why hire two actors when one can do the job?
** BackupTwin: Another variant where the twins are never on screen at the same time (as an excuse for a popular actor to come back.)
** EvilTwin: Particular case of this.
*** EvilBrunetteTwin
* {{Reincarnation}}: In the "looks just like the old me" variant.
* SurgicalImpersonation: An actor plays two characters, one of whom changes his face surgically to resemble the other.
* TalkingToHimself: Two (or more) characters voiced by the same voice actor, in a conversation with each other.
* TalkingToThemself: When two or more parts of a SplitPersonality engage in conversation.
* UncannyFamilyResemblance: Any family relation is played by the same actor.
* YouLookFamiliar: One actor plays two unrelated characters, within the same series, but (usually) different episodes.

See DoubleVision for a look at how they manage the trick of getting an actor on-screen more than once, when needed.

Understandably this happens a lot in animation, simply by giving the same voice actor multiple roles; see TalkingToHimself for that version. Not to be confused with TalkingToThemself, in which the actor plays different personalities of a single character in-story. For the ''other'' kind of "acting for two," see HideYourPregnancy.