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. He was placed in stasis 30,000 years ago. (SG1: "Revelations")
He was found by the Asgard and in 2002 he was being studied by Heimdall, who was trying to fix the Asgard's genetic cloning problems. (SG1: "Revelations")
It was eventually revealed that this branch of research came to a dead end, as did all the others. (SG1: "Unending")