High Quality Content by WIKIPEDIA articles! Jonathan J. "Jack" O`Neill is a fictional character in the Canadian-American military science fiction television series Stargate SG-1, Stargate Atlantis and Stargate Universe, three science fiction shows about military teams exploring the galaxy via a network of alien transportation devices. Played by American actor Richard Dean Anderson, O`Neill was a main character in the first eight seasons of Stargate SG-1 (1997–2005). O`Neill had a recurring role in Stargate Atlantis for the first three seasons (2004–2007), and he also appeared in the 2008 direct-to-DVD SG-1 film Stargate: Continuum as a minor character. Anderson reduced his character`s status in season six to spend more time with his family, eventually leaving the show after season eight, thereby removing himself from the status of main character.