Stargate SG-1 follows and expands upon the Egyptian mythologies presented in Stargate. In the Stargate universe, humans were enslaved and transported to habitable planets by the Goa'uld such as Ra and Apophis. For millennia, the Goa'uld harvested humanity, heavily influencing and spreading human cultures. As a result, Earth cultures such as those of the Aztecs, Mayans, Britons, the Norse, Mongols, Greeks, and Romans are found throughout the known habitable planets of the galaxy. Many well-known mythical locations such as Avalon, Camelot, and Atlantis are found, or have at one time existed.<br /><br />Presently, the Earth stargate (found at a dig site near Giza in 1928) is housed in a top-secret U.S. military base known as the SGC (Stargate Command) underneath Cheyenne Mountain. Col. Jack O'Neill (Anderson), Dr. Daniel Jackson (Shanks), Capt. Samantha Carter (Tapping) and Teal'c (Judge) compose the original SG-1 team (a few characters join and/or leave the team in later seasons). Along with 24 other SG teams, they venture to distant planets exploring the galaxy and searching for defenses from the Goa'uld, in the forms of technology and alliances with friendly advanced races.<br /><br />The parasitic Goa'uld use advanced technology to cast themselves as Egyptian Gods and are bent on galactic conquest and eternal worship. Throughout the first eight seasons, the Goa'uld are the primary antagonists. They are a race of highly intelligent, ruthless snake-like alien parasites capable of invading and controlling the bodies of other species, including humans. The original arch-enemy from this race was the System Lord Apophis (Peter Williams). Other System Lords, such as Baal and Anubis, play pivotal roles in the later seasons. In the ninth season a new villain emerges, the Ori. The Ori are advanced beings with unfathomable technology from another galaxy, also bent on galactic conquest and eternal worship. The introduction of the Ori accompanies a departure from the primary focus on Egyptian mythology into an exploration of the Arthurian mythology surrounding the Ori, their followers, and their enemies—the Ancients.