Trit

Trits were small, grey, hairless, monkey-like creatures with red eyes and remarkably unhairy ears. They were social parasites that switched places and assumed the bodies of people in power so that they could be served and pampered.

A Trit assumed the body of the Hussuloofian King, but was exposed as a bully and imposter when he failed to appreciate the Hussuloofian delicacy, the tripeberry brought to the royal court by the Eleventh Doctor as a gift. (DWAM: The King and the Tripeberry)