O'Brien (Reach)

Private O'Brien was a UNSC Marines aboard Reach Station Gamma, Dock 9, during the Fall of Reach.

Battle of Reach
O'Brien, along with Staff Sergeant Avery Johnson, PFC Wallace A. Jenkins, and Private Bisenti, were fighting a group of kig-yar when MCPO John-117 and PO2 Linda-058 boarded the station to destroy the logs of the ONI ship,.

Battle of Installation 04
"Glad you could make it, Chief... we saved some party favors just for you."

- O'Brien greets John-117 on board the Pillar of Autumn

He was picked up with Johnson and the 'Chief when they took a pelican and flew back to the Pillar of Autumn. When the Pillar of Autumn was boarded, John-117 recognized him (but could not remember his name) and saved him from a Kig-yar soldier. He was killed either when the Covenant boarded the Pillar of Autumn or during the Battle of Installation 04.