Omega

"I have been grievously wronged, Doctor, and now it is time for my vengeance!"

Omega was one of the key historical figures in the history of the Doctor’s home planet of Gallifrey. As galactic engineer, he created the Hand of Omega, which could turn stars into supernovas in order to harness their power to achieve time travel.

Believed killed in an experiment where a supernova collapsed into a black hole, Omega survived but was trapped in an anti-matter universe. Despite the Doctor and Time Lords lauding Omega as their “greatest hero”, Omega was eaten up with hatred of the Gallifreyans for abandoning him. He attempted to have the Third Doctor take his place in the anti-matter universe, not realising his new world had dissolved his physical body and he was surviving through sheer will alone.

Having failed to destroy the Time Lords, Omega attempted to use the Fifth Doctor’s biodata to create a new body for himself. The Doctor sabotaged his plan, rendering Omega’s new body unstable. It immediately began to decay and was converted into anti-matter by the Arc of Infinity.