Colonel sent by General Jack O'Neill at Stargate Command to relieve Dr. Elizabeth Weir of the Atlantis expedition. He brought reinforcements of troops and rail guns through the Stargate to defend Atlantis from an incoming attack of the Wraith. He was suspicious of Teyla Emmagan and her people and originally blocked them from vital areas of the city, but eventually the Athosians proved their worth and Everett decided to arm them.
Everett was a good friend of Colonel Marshall Sumner and at first did not care for John Sheppard -- who had been instructed by Sumner, in so many words, to kill him. During the siege of Atlantis he found out himself how Sumner died when a Wraith began feeding on his body.
Later, recovering in Atlantis's infirmary, he summoned Sheppard and told him that he wished the Major had been there for him the same way.
The Siege, Part 2 - Colonel Everett arrives to relieve Dr. Weir of her command and defend the city from the pending Wraith slaughter.
The Siege, Part 3 - Everett is attacked by a Wraith but manages to survive and is taken back to Earth through the Stargate.