A strong, no nonsense colonel in the United States Marine Corp, Sumner was the ranking military officer on the Atlantis expedition to the Pegasus Galaxy, though he was under the authority of the civilian expedition leader, Elizabeth Weir. Sumner was a stickler for rules, regulations, and the chain of command, and disliked Major John Sheppard for his record of disobeying orders to save two colleagues trapped behind enemy lines.
Sumner led a team to the planet Athos in the hopes of acquiring additional Zero Point Modules to power Atlantis, and there met the Athosians. He and some of his men, including Sergeant Bates and some Athosians, were captured by a Wraith culling beam and delivered to their hive ship on the Wraith homeworld. There he was interrogated by the Wraith Keeper for information regarding his homeworld, Earth. When he refused to relinquish further information the Keeper attempted to interrogate him by feeding on his life energy, taking years from his life. After a nod of approval during his torture, he was shot in a mercy killing by Sheppard.
Rising, Part 1 - Colonel Sumner travels to the Pegasus Galaxy, but is wary of Major John Sheppard's presence on the mission.
Rising, Part 2 - Sumner is captured by the Wraith and interrogated regarding this new human insurgence in their home galaxy. Major Sheppard shoots him in a mercy killing as the Keeper tortures him to death.