Thomas was a member of the United States Air Force. He was member of Jack O'Neill's squad when he was a Captain under the command of Colonel John Michaels. On a mission to East Germany in 1982 to extract a Russian spy, Michaels was killed. It was this mission that The Keeper made O'Neill relive when he was hooked into the Virtual reality pod and Teal'c took the role of Thomas. (SG1: "The Gamekeeper")