After having caused great destruction through the universe and diminishing their species to a small number, the Triskele divided themselves into three subspecies to moderate their actions. The Engineers were the creative side, the Uncreators the destructive part, and the Lawgiver was their free will and decision maker. Unlike the other two subspecies, there was only one Lawgiver. The Engineers and Uncreators could take no action without its approval.
When the Lawgiver was old and dying, the Engineer Prime went to Earth in 1930 to find a new one. Neither an Engineer or Uncreator could be the replacement, as then the new one would be biased towards those it had come from. When Peter Rathbone demanded the Triskele surrender to him and did not immediately agree, he shot and killed the Lawgiver, possibly psychically manipulated into doing so by the Uncreator Prime.
This freed the Uncreators, who turned more bestial from centuries of suppressed rage. Before they could cause severe damage, Lord Tamworth fought and defeated the Uncreator Prime. Trying to mentally influence Rathbone to kill Tamworth, Peter was able to gain enough control to shoot the Uncreator Prime instead.