Crewman Green was a male Human Starfleet enlisted crewmember in the 23rd century. He served in the command division aboard the USS Enterprise in 2266 under the command of Captain James T. Kirk, during the historic five-year mission.
That same year, Green accompanied Captain Kirk and Sturgeon to the surface of planet M-113 to investigate the death of Darnell, a crewman who had apparently been murdered recently. Kirk ordered Green to search for Nancy Crater, who had, in actuality, died some time before and been replaced by a creature able to hypnotically project an image of any individual it chose. Green came across this creature, and was subsequently attacked and killed. The creature then took on the appearance of Green and returned to the ship with the rest of the landing party. Eventually, Green's body was discovered, and it was realized that the creature had infiltrated the ship. (TOS: "The Man Trap")