Board Thread:Legitimate Canon Questions/@comment-27689910-20160128003129/@comment-4091815-20160128012542

Theo is a creation of the Dread Doctors. He wanted power, for undisclosed reasons, and saw the Dreads as an opportunity to achieve that. He allowed his sister to die to take her heart and become a chimera. The Dreads used him, and all the chimeras, in order to bring back the Beast. That's their goal.