The Master is a renegade Time Lord and the Doctor's arch-enemy and former childhood friend on Gallifrey. One of the Master's primary goals has always been to destroy the Doctor, Earth, and/or the entire Universe while acting on a number of diabolical schemes, no matter how petty, gross, or demented.As with the Doctor, the Master is able to regenerate into a new body, although his original regeneration cycle has long been exhausted. To extend his life past the normal Time Lord range, the Master has transferred his consciousness several times into other bodies until the High Council granted him a new regeneration cycle in exchange for his promised involvement in the Last Great Time War. As usual, he ran as soon as he was turned loose and hid as a human at the end of time under the alias of Professor Yana. He was later found by the Tenth Doctor and regenerated into a younger form that went on to be elected the UK's Prime Minister as John Saxon. Once he was vanquished in The End of Time, he didn't appear again until the after the Twelfth Doctor's regeneration, now as a female calling herself Missy (short for Mistress, the feminine form of Master). And, as before, despite the appearance of being destroyed/killed at the end of the episode, the Master/Missy will most likely reappear again in the future.The Master is the polar opposite of the Doctor in almost every respect. Though he retains a brilliant Time Lord mind and all of the Doctor's wit and cunning, he possessed two fatal character flaws - arrogance and exceptional vanity, which almost invariably leads to his downfall. However, it has been revealed that the Master hadn't always been like this: he and the Doctor were once good friends as children on Gallifrey. The Doctor believed that staring into the Time Vortex as an eight-year old child drove him insane and caused his personality to change. It was, in fact, during that later occasion that the High Council from Gallifrey's future sent the sound of the heartbeat of a Time Lord into the Master's mind, leading at least in part to his madness. Show less «