Donnell Guerin was a former Master Sergeant of the UNSC Marine Corps and ORION Project operative who turned to a life of crime following his discharge from the military. Originally a juvenile delinquent from the colony of Emerald Cove, he distinguished himself during his military career as a particularly cunning and creative fighter whose lack of formal education was compensated by a natural knack for the art of war. He participated in the SPARTAN-II Program as a combat instructor, pushing the child candidates to their limits while teaching them how to fight. His first and only battle of the Human-Covenant War saw him wounded in action and the combination of physical and psychological trauma was sufficient to merit an honorable discharge; however, he murdered a superior officer shortly aft