Green

Green was a crewman who served aboard the USS Enterprise in the 2260s. In 2266, Green accompanied Captain James T. Kirk to the surface of planet M-113 in an attempt to search for Nancy Crater, and during a search of the ruins he was killed by the M-113 creature.

The creature then took the form of Green and beamed back up to the Enterprise with the landing party. Once aboard, the creature kept the appearence of Green in order to search for more salt, and almost caught Yeoman Janice Rand. After a while, the creature abandoned the image of Green and instead assumed a form he could read from his prey's minds.

When Green's body was eventually discovered on the surface by Dr. Leonard H. McCoy and Captain Kirk, they realised that they were dealing with a threat that could take any form and eventually the creature was killed. (TOS episode: "The Man Trap").