The Asgard ancestor was a member of the Asgard race. He was aboard on the ancient Asgard ship whose navigational computer was damaged at some point, and the ship drifted across space.
The asgard put himself in stasis in 30,000 years, until the ship crashed on Adara II. In 2002 he was found by one Asgard descendant Heimdall. (SG1: "Revelations")