Chameloid

The Chameloids are a shapeshifting humanoid species which can alter their appearance to mimic other life forms at will; although they claim that such transformations take a lot of effort.

History
As of 2293, this species was already known to the Federation and to the Klingon Empire, although most people considered them nothing but myth. A criminal member of this species called Martia was captured by the Klingons and imprisoned in the frozen prison planetoid Rura Penthe.

Appearances

 * Star Trek VI: The Undiscovered Country (1991)