'Stargate Atlantis' follows the human-led Atlantis expedition, who established a base in an abandoned city of the Ancients in the Pegasus galaxy.
1. Joe Flanigan as John Sheppard
Sheppard is the ranking military officer on the Atlantis expedition; he starts out as an Air Force major and is later promoted to lieutenant colonel. An outstanding pilot able to fly just about anything, Sheppard is a maverick but easygoing and genial. His piloting ability and natural leadership skills make him invaluable even when he's on the outs with his superiors.
McKay is the (self-billed) resident genius of the expedition team, an astrophysicist with expertise on ancient civilization in general and the stargate system in particular. Despite his tendency to talk down to those who aren't as smart as he is (which is to say, everyone), McKay has the respect and even the love of his teammates. He can be a hypochondriac and has been known to catastrophize in a crisis, but his early nervousness about away missions melted gradually in to confidence in the field, making his a valuable member of Sheppard's off-world team. McKay first appeared in the 'Stargate SG-1' episode "48 Hours."
3. Rachel Luttrell as Teyla Emmagan
Teyla is a native of Athos and a hereditary leader of her people, where she developed several key talents: she can sense the Wraith, she is an expert at various forms of personal combat, and she has a knack for offensive strategy. She was at first slow to trust strangers, but after saving Sheppard's life, Teyla was in turn rescued from the Wraith by him, which was the beginning of a personal bond between them. She has since dedicated herself to helping the humans find friends and allies among the other races of the Pegasus Galaxy. She became a member of Sheppard's off-world team. Foretellings about the future role of the child she carried during season 4 brought her to the attention of the Wraith called Michael.
4. Jason Momoa as Ronon Dex
Ronon is a Satedan from the Pegasus Galaxy. He had been living as a kind of prey tracked by the Wraith for sport (a Runner); before that he had been a military officer, and was offered a place on the team by Sheppard for his natural abilities with combat and weaponry. He has self-healing abilities and is a formidable warrior, but while a man of few words he is kind, loyal, and not easily daunted. His ultimate motivations for working with the Atlantis team were at first unclear, but his bond of brotherhood with Sheppard and Teyla led him to find in Atlantis the home he no longer had.
5. Jewel Staite as Jennifer Keller
Dr. Keller became the chief medical officer of the Atlantis expedition after the sudden death of Dr. Carson Beckett (at the end of season 3). Though brilliant and accomplished, at first she felt unprepared for such a responsibility, and in her early handling of medical crises she seemed surprised at her successes. Her beauty and self-deprecating charm have attracted the attentions of many, including both Dr. McKay and Ronon.
Woolsey started out as a bureaucrat called in to second-guess decisions made by Stargate Command that led to the death of a team member (in the "Stargate SG-1' episode "Heroes: Part 2"). Later he became attached to the IOA, the international body overseeing the Stargate program, and as such had sporadic encounters with both SG-2 and Atlantis prior to being placed in charge of the expedition at the beginning of season 5. His background in law, faith in the efficacy of playing by the rules, and unshakable belief in civilian oversight of the military made him confident in the system, but once in charge he rapidly found himself in situations where the rulebook seemed to lead to disaster, causing him trepidation about his ability to command.
Dr. Beckett was the chief medical officer of the Atlantis mission, a proud Scot known for speaking his mind. His biological research has increased the understanding of alien races, in particular the Wraith, and led to a treatment that could convert a Wraith into a human. Beckett's no-nonsense manner has made him popular both with his colleagues and with fans of the show; Beckett's role was increased for season 2 and there was great outcry when his character was killed off toward the end of season 3. A clone created by Michael was discovered late in season 4, setting up several subsequent Carson episodes.
8. Amanda Tapping as Samantha Carter
Col. Carter, one of the original members of the SG-1 team, was trained as an astrophysicist and used her technical prowess to save her team, alien races, and the entire Earth many times over. During the escalating conflict with the Replicators, Carter was placed in charge of Atlantis (during season 4) and was successful in eliminating the Replicator threat and defeating the Wraith forces of Michael. Once this was accomplished, however, the IOA stepped in and reasserted civilian control of the mission, replacing her with Richard Woolsey.
9. Torri Higginson as Elizabeth Weir
Dr. Weir was a trained diplomat and served as the civilian commander of the Atlantis expedition, approving operations and conducting negotiations. Although committed to a nonviolent approach whenever possible, believing that the best way to stop the proliferation of weapons is to end the need for them, she was capable of doing what is necessary. Fatally wounded in a Replicator attack on the Atlantis base, Weir survived by using a nanotechnology therapy that made her able to stand head to head against the leader of the Replicators, but was forced to sacrifice herself for the destruction of their world; however, a version of Weir still exists. Dr. Weir was introduced in the SG-1 episode "Lost City" (where she was played by Jessica Steen).