Chameloid

Chameloids are a species of shapeshifters

In 2293 a Chameloid named Martia was hired to kill Captain James T. Kirk and Doctor Leonard H. McCoy after they were framed for the murder of the Klingon Chancellor Gorkon and sent to the prison world of Rura Penthe. Martia was killed by a Klingon whilst she was impersonating Kirk. (TOS movie: The Undiscovered Country)