A key figure in Time Lord history, Omega was a great scientist from the early days of Gallifrey who created the Eye of Harmony, the black hole from which all TARDISes draw their power. In achieving this, however, he was sucked into another black hole where he was trapped for eternity in an Anti-Matter world of his own making. After centuries, he only continued to exist through the strength of his will alone, although that didn't stop him trying to escape. The Doctor faced a maddened Omega, desperate to flee the black hole at whatever cost, in The Three Doctors and Arc of Infinity; thwarting him on both occasions. Oh well, maybe next time.