Thor

Thor (voiced by Michael Shanks) is the Supreme Commander of the Asgard Fleet and is first encountered in "Thor's Hammer" as a recorded hologram. Later, during Heru-ur's attack on Cimmeria in "Thor's Chariot", Dr. Daniel Jackson and (then-Captain) Samantha Carter, attempting to ask his help in saving the people from the System Lord's forces, entered the Hall of Thor's Wisdom, which was set up by the Asgard in order to gauge whether the people of Cimmeria had advanced enough in order to see them in their true form. Thanks to SG-1's artificial advancement, they soon discovered Thor as a being who looked uncannily like one of the Roswell Greys. Thor himself has commented that his race have visited the Tau'ri on many other occasions. The Asgard save Cimmeria but intially take on the view that the Tau'ri are still too young of a race to ally with against the Goa'uld. After Jack manages to accidentally get a library of Ancient knowledge downloaded into his brain ("The Fifth Race"), he creates a DIY version of a ZPM that allows him to dial the Stargate to an Asgard world in another galaxy and develops the beginnings of a friendship with the Asgard. In his own words, "They like [him]," also naming an advanced battle cruiser, The O'Neill after him. Thor also apparently thinks very highly of Major Carter, once enlisting her help and "less-advanced" ways of thinking in order to save the Asgard homeworld from an immediate threat by the Replicators. Thor has risked his life multiple times in order to save SG-1 and Earth from both the Goa'uld and the Replicators, apparently seeing the Tau'ri as a very worthy race for an alliance. That alliance proved useful for him as SG-1 has saved him on many occasions from the Replicators and once from Anubis himself.

Like the rest of his race, Thor is an assexual clone, incapable of cellular meiosis (sexual reproduction). This has allowed him to cheat death on multiple occasions, by means of downloading his conciousness into a newer, younger clone body, but also makes him vulnerable to the slow, genetic degredation being suffered by the rest of the Asgard.