Harper was a Major in the United States Marine Corps and also the leader of SG-5.



He traveled to P3X-439 with SG units 1, 3, and 5 to attempt to recover one of the Ancients' Repository of knowledge. He defended the Stargate alongside Colonel Albert Reynolds until the mission was completed, fighting off Al'kesh and Death Gliders sent by the Goa'uld Anubis. (SG1: "Lost City, Part 1")


When Vala Mal Doran was kidnapped by Athena, he coordinated people in the search of hospitals around the area in the hope that she was injured and could not contact Stargate Command. (SG1: "Memento Mori")

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