The Engineer Prime was the leader of the Engineer subspecies of the Triskele.
When the Lawgiver, who moderated the actions of the Engineers and Uncreators, was 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 biassed towards those it had come from. Initially believing that most of Earth were like the Uncreators, the Engineer Prime was unwilling to speak with anyone. The Engineer entered a trance with the medium Madame Zelda, who convinced the Engineer Prime that there were "higher forms" suitable for speaking with which lived on Earth. When the Engineer Prime's spaceship had crashed, Zelda worked as a "go-between" to re-establish contact with the Triskele flying saucer. The Engineer Prime was brought back on board the Triskele flying saucer, having reached it in the air using the R101 to avoid suspicion. When Peter Rathbone demanded the Triskele surrender to him and they 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.
The Engineers declared Tamworth as the new Lawgiver, a title he refused. He said he would advise them only, and help the Triskele find a new way. (AUDIO: Storm Warning)