Jack was a space mission commanding officer in 2210. He was a relative of Harry Kim, who referred to him as an uncle.
Harry once told the story of Uncle Jack to his crewmates on USS Voyager's senior staff. He recounted that Jack had commanded a deep-space mission to Beta Capricus. The journey took six months, his uncle piloting the spacecraft the entire time, as the rest of the personnel were in stasis. Upon their arrival, it turned out that the star Beta Capricus did not exist, its detectable emissions were nothing more than an electromagnetic echo of a distant galaxy. Jack did not wake his crew because there was nothing to do or see, and instead returned to the Sol system. When they arrived home from their year-long journey, Jack brought the crew out of stasis and they wondered why they had not yet left Earth's orbit. (VOY: "11:59")
This individual was only mentioned in dialogue.