Walker was an Airman in the United States Air Force. He was stationed on one of the Tau'ri's off-world bases, the Gamma Site. He and SSgt. McLeod guided International Oversight Advisory Representatives and SG-1 to an unmanned research station near the base. On the path to the station the group was attacked by a swarm of R-75. SG-1 succeeded in stopping them by sliding into soil. Walker then led them into a cave where they could take protection from the bugs, as R-75 were unable to dig through mountainous terrain. During the night, he guarded the cave while the others slept.
Mitchell glanced at him and tried to contact the Gamma Site but received no response. After Mitchell left the cave, Walker scratched his neck, and a small R-75 bug crept underneath his skin. The next morning he was absent from his post at the front of the cave, and Teal'c, Dr. Daniel Jackson and Lt. Colonel Cameron Mitchell went searching for him. Daniel then discovered Walker's dead body and hundred of bugs poured out. (SG1: "The Scourge")