Private Walker is the Heavy weapons Specialist of Corporal Harland's unit. He took part in the Battle of Sigma Octanus IV. However, after the encounter with the Hunters, which killed most of the unit including CO Second Lieutenant McCasky, and fleeing a fight with a small unit of Grunts, Walker was frozen with fear and had a mental breakdown. Walker's breakdown would have cost his squad their lives had Private Cochran not taken the initiative to shoot down a couple of pursuing Banshees. Walker's breakdown slowly vanished upon returning to Alpha Headquarters, near the city Côte d'Azur, and Harland eventually regained trust of Walker and allowed him to fight again. He and his team were later evacuated when the SPARTAN-IIs destroyed all of the Covenant forces using a HAVOK Nuclear Warhead.
- Halo: The Fall of Reach (First appearance)