Heimdall (Stargate)

The Asgard are a highly advanced, fictional extraterrestrial race in the science fiction series Stargate SG-1 and Stargate Atlantis. They are first mentioned in the episode "Thor's Hammer", and first seen in "Thor's Chariot". In the series, the Asgard gave rise to Norse mythology on Earth, as well as accounts of the Roswell "Greys". Due to their technological Prowess, the Asgard are critical allies in Earth's fight against the Goa'uld, and later the Ori. The Asgard characters on the show are realized through a combination of puppets and computer-generated imagery.

The episode "The Fifth Race" establishes that the Asgard inhabit the galaxy of Ida, and that they were once part of an alliance of four great races with the Ancients, Nox, and Furlings. In ancient times, the Asgard visited Earth, posing as the gods of Norse mythology. Norse legends tell of how they protected the humans against the "Ettins" (Goa'uld). The Asgard protect a number of planets in the Milky Way from Goa'uld attack under the Protected Planets Treaty. In the time of Stargate SG-1, the Asgard are a dying race. Having lost the capacity for sexual reproduction, they perpetuate themselves by transferring their minds into successive cloned bodies. Repeated generations of cloning has led to an irreversible degeneration of the Asgard genome. A 30,000-year-old Asgard ancestor is depicted in "Revelations", showing a more human-like appearance.

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Wikipedia