I'm going to go out on a limb here and say that as a spin off, Atlantis has done much more than its parent series, Stargate SG1, by introducing a new cast of characters who give us more of what the essence of Stargate is - funny, serious, sad, and epic at the same time.
The premise of Atlantis is a continuation from the "Lost City" two-parter that ended Season 7 of SG1. Following further examination of the cave in which the Antarctic Stargate and Ayiana were found, Jackson discovers that the address to Atlantis is eight-symbol - that is, it is located in a whole new galaxy. Dr. Weir, the former head of the SGC, played by Tori Higginson, is appointed the head of the expedition, and some old favorites such as Dr. Rodney McKay return to the scene.
The newcomers are no less handy. Major (and later Colonel) John Sheppard, played by Joe Flanigan, is the junior (and then later senior) military leader of the Atlantis Expedition and possesses an uncanny talent to pilot or use anything that requires the use of the Ancient Technology Activation gene. Carson Beckett played by Paul McGillion, is the medical officer aboard the ship and has become a fan favorite for innumerable reasons.
Upon their arrival, they discover that Atlantis has almost completely run out of power and has been submerged under the sea. Not having enough power to activate a gate back home, they start looking for a way out within the new galaxy, and discover the Athosians, who tell them of a new enemy, the Wraith. Their leader, Teyla Emmagan (Rachel Luttrell), recognizes them as technological descendants of the Ancestors, as they refer to the Lantean Ancients, and believes that they have the power to stop them. Soon after, the team discover that the Wraith are waking up in droves and are a far greater threat than they envisioned - they were responsible for the extinction of the Ancients within the Pegasus galaxy. Much of the series revolves around trying to find ways to combat and destroy the Wraith.
Later on, new enemies are introduced, including a new variant of the human form replicators created by the Asgard - only this time they have very powerful Ancient technology which rivals that of the original Ancients. Later on, Ronon Dex (Jason Momoa), a Satedan fighting against the Wraith in vengeance for the destruction of his homeworld and the murder of his people, joins the Atlantis team.
A must see.
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