O'Brien (Heian)

"I don't miss! I never miss!"

- O'Brian

O'Brian was a member of the UNSC Marine Corps who participated in the Human-Covenant War. He was an Orbital Drop Shock Trooper assigned to the Marine contingent aboard the Destroyer DD-993.

Assassination
He and his fellow Helljumpers were charged with attacking a Covenant force on an unnamed planet, in which O'Brian was to serve as the backup sniper. He felt this was an insult to his abilities and was even more shocked to learn that a Spartan-II was the primary shooter. As soon as they were deployed his pod was sent crashing to a nearby cliff and fell into a swamp. The fall damaged the oxygen tank and with the pod sinking, it would of killed him.

Cortez and Dutch tried to hurry to save him but stop short due to the thick mud. Cal calmly walks to the pod, and with some effort, lifts the pod and tosses it out of the swamp. She then pries the door loose to get him out alive.

O'Brian is shocked by the sudden action and is not happy with the loss of Checkman. Along the way, he needled Cal whenever the chance came, showing his contempt for the Spartan despite the fact that without Cal's help he would have died in his pod earlier.

During the operation, he is attacked by a Brute Chieftain wielding a Gravity Hammer while attempting to kill a Grunt he alerted. However, before the Gravity Hammer struck, Cal-141 saves him, but O'Brian winds up hanging over a waterfall as he watches the Spartan battle the creature. O'Brian loses his Sniper Rifle in the process along with his SMG, leaving him weaponless.

Cal saves him again when she pulls him up off the waterfall. However, he seemed unappreciative as he yelled at her to put him down, and then snaps at Dutch who told him to quiet down before alerting anymore Covenant patrols. His anger and contempt towards Cal grows a bit hotter when Dutch reminds him that Cal saved his life twice already and should thank the Spartan.

The group soon makes its way to where they're taking the shot just as the shuttle of the Prophet was touching down. However, just the mission was reaching the end, the Chieftain from earlier returns, and is about to kill O'Brian before Cal saves him again at the last second and for the last time, taking the blow from the Chieftain's Gravity Hammer.

The ODSTs tackled the Chieftain to the ground and Dutch shoots the Brute in the face repeatedly with his SMG. O'Brian is then shocked to discover that Cal was a woman and not a man as Cortez removes Cal's helmet to assess the extent of the Spartan's injuries. Cal, realizing that she can no longer function as a sniper due to extent of her injuries then yells to O'Brian to take the shot. At first he hesitates, but takes up the Sniper rifle and kills the Prophet.

He is then witness to the sight of Cal's last moments until she died. O'Brian is later seen back on the Destroyer, not saying a word before and after the rest of the squad angrily scold Berger who had mocked Cal's abilities in battle, and thinking deeply about how Cal continually saved his life.

Trivia

 * O'Brian bears a striking resemblance to Spike Spiegal from the anime series, Cowboy Bebop.