Master, The – Enemy of The Doctor and rival Time Lord. The Master and the Doctor had once been friends [OS: The Sea Devils], before the Master turned Renegade. Motivated primarily by greed, the Master’s plots typically involved selling his services to invading aliens as a covert agent [OS: Terror of the Autons], or seeking powerful weapons with which to extort the galactic powers [OS: Colony in Space]. His last incarnation is left badly disfigured and near-death in a fight with Susan Campbell (neé Foreman) [PDA: Legacy of the Daleks]. Having exhausted his regeneration cycle, he became obsessed with cosmic powers including the Eye of Harmony [OS: The Deadly Assassin], the Source [OS: The Keeper of Traken], the Xeraphin [OS: Time-Flight], the Flames of Karn [OS: Planet of Fire] and the regenerative powers of the Cheetah People [OS: Survival], finding enough partial success to extend his lifespan and usurp the body of the Trakenite scientist Tremas. He eventually returns to his original modus operandi by working as an agent of the Tzin, who pay him for his service by using their technology to grant him a new regeneration cycle [NA: First Frontier]. Some time later, a possibly reformed Master serves as Time Lord president during the Time War [WDA: The Ancestor Cell], but becomes corrupted by the War Lords, adopting the title of War King [BF: Liberation]. Some time between the fall of Arcadia and the end of the war, the Master becomes aware of the War Doctor‘s plans to end the war, and uses the power of the Sword of Rassilon to escape the Temporal Event Horizon of the war [TDA: The Gallifrey Chronicles]. He eventually resumed his criminal ways, making several attempts to sell Earth to invading aliens [US: The House-Guest], ultimately making a deal with the Morthrai [US: Loving the Alien]. To this end, the Master opened a Warp Shunt to the Morthrai homeworld using his TARDIS. He was apparently killed when the Doctor destroyed both TARDISes via Time Ram to close the Warp Shunt.
Are you hiding, somewhere behind those eyes? -- Icehouse, Electric Blue