The Collaborative International Dictionary of English v.0.48:
Mimicker \Mim"ick*er\, n. 1. One who mimics; a mimic. [1913 Webster] 2. (Zool.) An animal which imitates something else, in form or habits. [1913 Webster]WordNet (r) 3.0 (2006):
mimicker n 1: someone who mimics (especially an actor or actress) [syn: mimic, mimicker]