John "Jack" Swigert is an astronaut.
Sometime during or prior to 1970, Jack joined NASA. In 1970, Jack was promoted to the prime crew for the Apollo 13 mission to the moon. In preparation for his mission, he was examined by Eobard Thawne, who was pretending to be a physician. Eobard later assumed Jack's identity (presumably with the use of a special device) and replaced him in the Apollo 13 mission. It is unknown what happened to Jack afterwards.