Male humanoid Replicator, first to emerge from the intelligence of the Replicators after they took over the Asgard planet Halla. First represented the culmination of malevolence and hatred for anything not based on keron technology. He was responsible for stopping and reversing the time-dilation device, as there was a microscopic crack in the neutronium shell that he could manipulate.
First was intent on probing Jack O'Neill's mind and gaining intelligence all the worlds the team had ever visited. He and O'Neill traveled to all of SG-1's missions, presumably so he could mark planets for invasion when the Replicator army reached its apex of warriors.
Unnatural Selection - First and the rest of his Replicator android brethren block SG-1's exit from the ancient Asgard facility on Halla, eager to enter the team's minds and plot future exploits for the conquering of planets.