Trit
From Tardis Wiki, the free Doctor Who reference
Trit’s are small grey, hairless, monkey-like creatures with red eyes and remarkably unhairy ears. They are social parasites that switch places and assume the bodies of people in power so that they can be served and pampered.
When a Trit assumes the body of the Hussuloofian King, he is exposed as a bully and imposter when he fails to appreciate the Hussuloofian delicacy the tripeberry brought to the royal court by the Doctor as a gift. (DWAM: The King and the Tripeberry)