High Councilor of the Asuran people, and the first of the molecular machines that assembled themselves into a likeness of their creators -- the Ancients. It is likely because of his seniority, and apparent inability to die, that he had remained High Councilor for over ten thousand years.
Like all Asurans, Oberoth was governed by the same base aggression that was encoded into their governing programming from the beginning when the Ancients wished to make them into a devastating weapon. When the Ancients decided to abandon their creation they dispatched countless warships to where they had thrived and destroyed their civilization in an aerial assault. But Oberoth and others managed to survive -- or replicate.
Oberoth had no interest in having the base aggression deleted from his or his people's personalities. Additionally, he had no immediate interest in following the Ancients in their path to ascension, as the aggressive subroutines may be the only hindrance to this evolutionary leap. It was this aggression that eventually led him back to Lantea where he intended to annihilate the lost city from the face of the Pegasus Galaxy in a retributive rage.
Oberoth accused the Ancient Lanteans of arrogance, just as he claimed in a lie, which led them to greatly underestimate the Wraith. During a visit of the Atlantis expedition he tried to appease Dr. Elizabeth Weir by informing her that eradication of the Wraith was among his people's long-term goals. But because the Asurans had never had difficulty with the life-sucking race, this was doubtful.
Oberoth and many of his brethren were destroyed aboard a copy of Atlantis that had arrived in Lantean orbit to obliterate the actual city of the Ancients when Dr. Rodney McKay rigged three Zero Point Modules to overload. Considering his long-lasting history, it was extremely unlikely that he was truly gone.
Progeny - Oberoth welcomes the Atlantis expedition to Asuras to satisfy his people's occasional curiosity -- but is not inclined to let them depart after he discovers they may possess information that will lead his people back to Atlantis.
First Strike - Oberoth communicates briefly with Elizabeth Weir via a video transmission, having ordered a devastating counter-attack on Atlantis.
Lifeline - Oberoth responds personally when Sheppard's team infiltrates his city, but is stopped by Dr. Weir. Now part Replicator herself, she invades his mind and keeps him occupied, distracting him with a fake scenario in which the team is captured.