U.S. Marine Colonel Dillon Everett was sent through the SGC Stargate to Atlantis to lead the heavily-armed Marines in the battle against the Wraith, an alien race encountered by the Atlantis Expedition Team on their first off-world mission. Col. Everett took command of the base by orders of Gen. Jack O'Neill. Dillon had objections to John Sheppard, as he was a friend of Marshall Sumner. During the Wraith attack, Everett was fed upon by a Wraith, but it was interrupted. Everett, however, aged considerably. When John Sheppard visited him in the infirmary, he told Sheppard that he had done the right thing with Sumner, and wished that Sheppard had been there to do it for him. (SGA: "The Siege, Part 2", "The Siege, Part 3")
Colonel Everett also posses the Ancient Technology Activation Gene by Gene Therapy.