|Played By:||Robert Patrick|
A no nonsense colonel in the US Air Force, Colonel Marshall Sumner was the ranking military officer that went on the Atlantis Expedition. Once on the other side, Sumner and his men soon realised that the city was losing power. Hoping to find refuge on another planet for the expedition, Sumner led a team through the gate to determine the threat and the possibility of relocating the expedition to the planet as well as the availability of ZPM's to power Atlantis.
Unfriendly towards John Sheppard who had a record for disregarding authority, Sumner reluctantly took him under his command. When on the planet, they met the Athosians who welcomed them, however soon they were attacked by the Wraith who had come to the planet to 'cull' the humans. In the attack, Sumner along with many others from his team as well as Athosians were taken back to the hive ship.
On the Wraith Hive Ship, Sumner tried to talk to their abductors, however taken before the Wraith Queen, he was tortured for information and was forced to tell them about Earth. Having the life sucked out of him, he was fortunate to have Sheppard free him from the pain and torture when he shot him.
When the Atlantis Expedition discovered a frozen Elizabeth Weir in Atlantis, she told them of an alternative time line in which Marshall Sumner was unfortunate enough to drown when the shields of Atlantis failed.