Steven Caldwell (Stargate)

The characters from the Canadian military science fiction television series Stargate Atlantis were created by Brad Wright and Robert C. Cooper. The series follows the adventures of a human expedition to the lost city of Atlantis in the Pegasus Galaxy. The Stargate has brought humanity into contact with other cultures, including new and powerful enemies: the Wraith, the Genii, and later the Asurans and a lost tribe of Asgard, all while trying to uncover the secrets the Ancients left behind.

Stargate Atlantis has a small cast, amounting to ten main cast actors over its five-season run. Most characters are introduced in outgoing expeditions outside the city of Atlantis.

John Sheppard played by Joe Flanigan is a USAF Lieutenant Colonel (ranked major in season 1). He is an experienced and a talented US Air Force Officer in Afghanistan, though his reputation is somewhat tarnished when he disobeyed a direct order in an unsuccessful attempt to save the lives of several US servicemen. When called upon to transport Brigadier General Jack O'Neill into the research base that has been established at the nearby Ancient defense facility, Sheppard inadvertently discovers that he not only has the ATA gene (the genetic factor necessary to activate Ancient technology), but that he is naturally proficient at using it. After some doubts, he finally joins the expedition to Atlantis, although Colonel Marshall Sumner makes it clear he is not pleased about Sheppard's involvement in the mission. In Season 1, Sheppard serves as both a Major and later also becomes the military commander following Colonel Sumner's death. In Season 2, Sheppard is eventually promoted to Lieutenant Colonel and still remains as Atlantis's military commander with Sheppard serving as the team leader for the Atlantis Expedition's team, the First Atlantis Reconnaissance Team or AR-1.

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Wikipedia