The Master

The Master is the Doctor's opposite, though their histories contain many similarities: both studied together at the Time Lord academy, each stealing a TARDIS to roam the universe. The Master, whose intellect is equal to the Doctor's used his talents to dominate and destroy, perfecting his hypnotic powers and his charm. The two have clashed frequently on Earth during the third Doctor's exile, the Master lead many invasions by the Daleks, the Autons and the Cybermen. Having reached his cycle of regenerations, he had become a hideously deformed and cowled skeleton, obsessed by hate and revenge, who struggled insanely to sustain his life cycle, almost destroying Gallifrey in his attempt. Grimly clinging t life, he became stranded on Traken as a Melkur, gathering power until he was able to escape, stealing the body of Tremas. In his new body, the Master adopted many different disguises to conceal his identity. Although the Master was unusually dispatched by the Time Lords to aid the five Doctors in the Death Zone on Gallifrey, he used this situation to his advantage, by seeking the power of Rassilon and immortality. He remains one of the Doctor's most dedicate enemies.

The Master was in Terror of The Autons, The Mind of Evil, The Claws of Axos, Colony In Space, The Dæmons, The Sea Devils, The Time Monster, Frontier In Space, The Deadly Assassin, The Keeper of Traken, Logopolis, Castrovalva, Time-Flight, The King's Demons, The Five Doctors, Planet of Fire, Caves of Androzani (as a memory), The Mark of The Rani, The Trail of a Time Lord-The Ultimate Foe, Survival.