Template:Human Character Infobox Private O'Brien was one of the UNSC Marines aboard Reach Station Gamma, Dock 9, above Reach. He, along with Sergeant Johnson, PFC Jenkins, and Private Bisenti, were there fighting a group of Jackals when Spartan-117 and Spartan-058 boarded the station to destroy the logs of the ONI Prowler Circumference. He was picked up with Johnson and the Chief when they took a Pelican and flew back to the Pillar of Autumn. He was killed either when the Covenant boarded the Pillar of Autumn or during the events on Installation 04. When the Pillar of Autumn was boarded, the Chief recognized him (but did not remember his name) and saved him from a jackal.