O'Neill may refer to:
- Colonel/Brigadier General/Major General/Lieutenant General Jack O'Neill, former SG-1 and Stargate Command leader, current Homeworld Command headmaster (Stargate, Stargate SG-1, Stargate Atlantis, Stargate: Continuum, Stargate Universe).
- Jack O'Neills from alternate realities:
- Brigadier General Jack O'Neill, commander of the SGA (SG1: "There But For the Grace of God").
- Colonel Jack O'Neill, late Dr. Samantha Carter's husband, killed by an alternate Teal'c (SG1: "Point of View").
- General Jack O'Neill, still commander of the SGC in an alternate reality (SG1: "Ripple Effect").
- Colonel Jack O'Neill, presumed still frozen in the Antarctic outpost after the battle of Antarctica in an alternate reality where the Stargate Program is public (SG1: "The Road Not Taken").
- Jack O'Neills from alternate timelines:
- Colonel Jack O'Neill, retired soon after an encounter with the Aschen.
- Brigadier General Jack O'Neill, trapped and killed in Ancient Egypt in 3,000 BC after attempting to retrieve a Zero point module (SG1: "Moebius", Part 1).
- Colonel Jack O'Neill, a retired US military coming back to SGC in order to fix the timeline (SG1: "Moebius", Part 1, "Moebius", Part 2).
- Major General Jack O'Neill, killed by a Baal clone (Stargate: Continuum).
- Colonel Jack O'Neill, a Special Forces operative (Stargate: Continuum).
- Jack O'Neills from hallucinations:
- Other Jack O'Neills:
- Sara O'Neill, O'Neill's ex-wife (Stargate, SG1: "Cold Lazarus").
- Charlie O'Neill, Jack and Sara O'Neill's deceased son (Stargate, SG1: "Cold Lazarus").
- Colonel O'Neil (with only one "L"), a US military who has no sense of humour at all (SG1: "Secrets").
- Jack O'Neill's house, former O'Neill's residence.
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