The Master is one of Doctor Who's most deadly enemies. A fellow Time Lord from Gallifrey, The Master attended the Time Lord Academy with the Doctor. Both of them were rebels, dissatisfied with the strictures of the Gallifreyan society. In the case of the Doctor, this dissatisfaction was caused by wanderlust and desire for adventure. In the case of The Master, it was a desire for power and to wreak havoc that drove him. They each stole a TARDIS and became outcasts from Gallifrey and the Time Lord community.

The Master is evil, but not in a mindless way like many of the Doctor's other enemies. He is extremely smart and cunning. He enjoys causing chaos and takes pleasure in having the Doctor as a nemesis. He desires power and is consumed with a desire to destroy the Doctor, who imrisoned him temporarily on Earth (Terror of the Autons, 1971) and has thwarted many of his schemes. The Master's favored weapon is a short, black rod called the Tissue Compression Eliminator, which reduces a person into a tiny, shrunken corpse. He has also been known to use the inherent mental powers of the Time Lords in order to control the minds of others, forcing them to do his bidding. His TARDIS (unlike that of the Doctor) is usually fully functional (including its chameleon circuit, a component with which the Doctor has had extensive problems), and it is even a more recent model than the one used by the Doctor.

The Master is one of only a few Time Lords the Doctor has faced, and is by far the Time Lord he has most frequently encountered. A few of the others are:

The Master appeared in the following television episodes:

The Master was played by five men:

Sources:
http://www.whotopia.co.uk/drwho.htm
http://www.mentalis.f9.co.uk/DWID/
http://www.tvtome.com/tvtome/servlet/ShowMainServlet/showid-355
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