The main protagonist and main antagonist of Spec Ops: The Line.

Captain Martin Walker is the commander of the Delta Force of the U.S. Army, consisting of Lieutenant Adams and Sergeant Lugo. His group is tasked with finding survivors remaining in Dubai after receiving a message from Colonel John Conrad describing his failed attempt to evacuate the city's residents.

Walker shows great respect for Conrad and has expressed a strong sense of trust in him for a long time. As the game progresses, Walker's mental health gradually begins to deteriorate due to the psychological stress caused by the war crimes he and his team commit in the chaos of battles and due to disinformation.