- See O'Neill for other articles with titles that contain, either by relationship or by coincidence, this character's surname.
- This page details O'Neil in the primary universe; for the O'Neil in the Kelvin timeline created by Nero's temporal incursion, see O'Neill (Kelvin timeline).
O'Neil was a Human male who served in Starfleet in the 23rd century. By the 2260s, O'Neil had earned the rank of lieutenant and was stationed aboard the USS Enterprise, under the command of Captain James T. Kirk.
In 2267, O'Neil accompanied Hikaru Sulu's landing party to the surface of Beta III to investigate the disappearance of the USS Archon a century earlier. Soon after beaming down, the party found themselves being pursued by the lawgivers, who enforced the will of Landru.
Although, the rest of the landing party were beamed back to the ship, O'Neil fled and he was eventually caught and "absorbed" by the lawgivers. Thankfully, O'Neil was eventually returned to normal when a second landing party, led by Captain James T. Kirk, was able to destroy Landru. (TOS episode: "The Return of the Archons")
- The novelization of this episode spells O'Neil's name as O'Neill. The comic adaptation lists him as O'Neal.
In 2268, O'Neil served as the transporter officer on duty when the landing party beamed over to the USS Defiant. During the subsequent attack by the Tholians, O'Neil attempted to repair the transporter, but needed Montgomery Scott's assistance. (TOS episode: "The Tholian Web")
When Kirk was recovered after his time in interphase, he recognized O'Neil at the transporter, recalling that he was an engineering technician serving under Montgomery Scott. (VAN novel: In Tempest's Wake)
- TOS episode: "The Return of the Archons"
- TOS episode: "The Tholian Web"
- VAN novel: In Tempest's Wake