Jack O'Neill was born in Chicago, Illinois, but spent the last of his childhood living with his grandfather in Minnesota. During his early life, he had a problem with drug addiction, but thanks to his grandfather's influence he straightened out his life. He became an officer in the USAF, where, despite being an excellent combat pilot, worked mostly on the ground with USAF Special Operations Forces. On one covert intelligence mission, Jack parachuted alone into Iraq, where he broke eight bones (if you count skull fractures) because his parachute opened late. Despite his injuries, Jack managed to make it out of Iraq safely. While working Spec-Ops, Jack married his wife, Sara, and she bore him a son, Charles. In 1994, Charlie accidentally shot himself with Jack's personal firearm and died. This tragedy hit both Jack and Sara hard. Jack found himself unable to communicate with Sara any more, and he was growing suicidal. Jack's compassionate leave was cut short when Daniel Jackson managed to get the stargate working, and Jack was recalled to lead the first team through it. On this mission Jack's team encountered one of Earth's oldest enemies, the goa'uld Ra. Jack and Daniel managed to get a nuclear device aboard Ra's ship and destroy him, and Jack returned with all the team survivors save Daniel. On his return, Jack had somehow lost much of his despondency, but it was too late for his marriage. Sara filed for divorce. Jack remained with the Stargate Program only a short while, then retired from the USAF.
When the goa'uld Apophis staged a raid through the stargate, Jack was recalled to lead a return mission to Abydos, when he recovered Daniel Jackson. Upon his return, Jack found that a new Stargate Command (SGC) had been formed with 9 SG teams to perform reconnaissance through the stargate. Jack O'Neill had been slated to lead the flagship team, SG-1. Jack led SG-1 for seven years. During that time, he and his team made first-contact for Earth with many other races among the stars, discovered new threats, and saved the Earth from destruction numerous times. While leading the team, Jack O'Neill found himself developing feelings for team member Samantha Carter. Because of regulations, Jack never acted on these feelings, but they did occasionally influence him. His only other relationships over this time period were a brief dalliance with Argosian (from P3X-8596) Kynthia, brought on by a local aphrodisiac, and a more serious relationship with Laira when he became trapped on P5C-768 (Edora) for over three months, and it looked like he wouldn't be rescued in his own lifetime. Jack was a headstrong leader, and was very nearly brought up on insubordination charges more than once. He also made a few enemies, not the least of which was Senator Robert Kinsey. During his tenure as SG-1's leader, Jack also managed to deal severe blows to the rogue NID operations that Kinsey helped support.
Twice while leading SG-1 Jack was implanted with a goa'uld/tok'ra symbiote. The first, a goa'uld implanted by Hathor, fled his body and died when a Tok'ra operative put Jack in a cryogenic sleep chamber. This goa'uld was not in Jack long enough to ever gain control of him. The second was the Tok'ra Kanaan, implanted to save Jack's life from an ancient plague. Kanaan left Jack as host during an attempted rescue of a human slave of Baal's. Because neither symbiote died in Jack, he wasn't left with naqahdah in his bloodstream and did not retain the abilities to use goa'uld technology or detect goa'uld.
After seven years running SG-1, Jack was promoted to Brigadier General and placed in command of the SGC itself. Lieutenant Colonel Samantha Carter took over his leadership of SG-1. Though his command style differed radically from that of General Hammond, Jack proved a very able commander, seeing the SGC through some of Earth's most dire moments.
One year later, Jack was promoted to Major General and moved to Washington DC to work with the Department of Homeworld Security. Jack handpicked Major General Hank Landry to be his successor in command of the SGC.
Jack O'Neil was originally portrayed by Kurt Russell in the movie Stargate. In the movie, the name was spelled 'Jack O'Neil', and his wife and son were 'Sarah' and 'Tyler'. Kurt Russel's portrayal was of a stern, by-the-book military man, made sterner by recent tragedy. Richard Dean Anderson portrayed Jack O'Neill for the series Stargate SG-1, and the spelling of his name was changed to 'O'Neill', and his wife and son's names were 'Sara' and 'Charlie'. His portrayal was of a much more humorous Jack O'Neill, who was often insubordinate. Christopher Judge also portrayed Jack O'Neill (in Teal'c), and Michael Shanks portrayed Jack O'Neill (in Daniel Jackson).
Richard Dean Anderson has been a part of the regular cast for seasons 1 through 8, and included in the title credits for all episodes for those seasons. However, he did not appear in Nightwalkers, Resurrection, or New Order Part 1. He appeared in Moebius Part 1, but not as Jack O'Neill, but rather as Jack O'Neill (Alternate-6) and Jack O'Neill (Alternate-7), alternate versions from time lines other than that carried on by the series. And, in Inauguration and Disclosure, he appeared in no new footage, but did appear in excerpts from previous episodes. Richard Dean Anderson has also portrayed Jack in the Pilot for Stargate: Atlantis as a guest star.