O Donnell was a security guard stationed at Pelvanida Research Base.
His character sheet posted by VT-Pilot reads as follows:
Name: Sgt. O Donnell
Specializations: O Donnell is a heavy infantry man. He knows how to use crew served weapons and is great with explosives. He uses a Kriss V .45 caliber SMG and a Barret M468 with an ACOG scope. He carries a handful of grenades. He wears standard heavy duty body armor and his helmet has a built in comm system.
Powers/Cybernetic enhancement: None
Personality: O Doneel, commonly called OD, served with the British SAS. He was transferred to the facility by his own request, seeking some time off and an easy assignment. Unfortuneately things didn't go as planned. He's a cool and calm minded soldier. Preferring to strike first and leave no survivors.
O Donnell fought the terrorists on his own for a decent length of the invasion before finally meeting up with the rest of the resistance group. When the teammates were interrogating a terrorist, he offered to torture the man for information.
Later, when the team encountered Tersian, O Donnell was so enraged by the scientist's casual disregard for Dragore Wing's well-being that he cracked the man's skull with his rifle butt. (Darwin's Soldiers)