The Collaborative International Dictionary of English v.0.48:

Impersonator \Im*per"son*a`tor\, n.
   One who impersonates; an actor; a mimic.
   [1913 Webster]

WordNet (r) 3.0 (2006):

impersonator
    n 1: someone who (fraudulently) assumes the appearance of
         another [syn: impersonator, imitator]

Moby Thesaurus II by Grady Ward, 1.0:

95 Moby Thesaurus words for "impersonator":
   ape, artist, artiste, belly dancer, blagueur, bluff, bluffer,
   burlesque queen, charlatan, chorine, chorus boy, chorus girl,
   conformist, conjurer, copier, copycat, copyist, coryphee,
   counterfeiter, cuckoo, dancer, dancing girl, dissembler,
   dissimulator, ecdysiast, echo, echoer, echoist, entertainer,
   exotic dancer, fake, faker, female impersonator, forger,
   fourflusher, fraud, geisha, geisha girl, guisard, guiser, hoofer,
   humbug, hypocrite, imitator, impostor, incognita, incognito,
   magician, malingerer, masker, masquerader, mime, mimer, mimic,
   mimicker, mocker, mockingbird, monkey, mountebank, mummer,
   musician, nautch girl, parrot, peeler, performer, phony,
   plagiarist, playactor, player, poll-parrot, polly, polly-parrot,
   poser, poseur, prestidigitator, pretender, public entertainer,
   quack, quacksalver, quackster, ringer, saltimbanco, sham, shammer,
   sheep, show girl, simulator, singer, stripper, stripteaser,
   stripteuse, thespian, trouper, vaudevillian, vaudevillist