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Gallifreyan scientist who, along with Rassilon, discovered the secrets of time travel and enabled members of his people to become Time Lords. Omega detonated the heart of the black hole that empowered Rassilon’s machines but was thought to have died in the explosion.
In fact he was flung into the world of anti-matter, his body decaying until there was nothing left of him but his will. He was thought to have been finally destroyed when, after trying to destroy Gallifrey, the combined powers of the first three Doctors destroyed his world. However, he survived and later tried to molecularly bond with the Doctor and take over his body. Again, Omega was defeated, apparently once and for all.
A stellar manipulator used by the Time Lords, the Hand of Omega, was named in his honour.