Crewman Rainer was a Starfleet security serviceman assigned to the USS Enterprise in 2270.
In 2270, he accompanied Captain James T. Kirk, Commander Spock, and Dr. Leonard McCoy to the surface of the Klingon colony world Tarnak II. He was assigned to scout the perimeter of the destroyed colony along with Crewmen Hornick and Washington. Unfortunately, the three security men were killed by Klingons under the command of Kang. (TOS comic: "The Chosen")