The Master is the arch nemesis of the Doctor. He was originally called Koschei. Like the Doctor, he's a Time Lord from Gallifrey, from the House of Oakdown, and was once childhood friends and colleagues with the Doctor. Both were bullied by a boy named Torvic as children. Because of another event in their childhood, the Doctor feels somewhat responsible for The Master. Where the Doctor believes in exploration, The Master believes in power and dominance. His evil can be traced back to an actual cause, part of someone else's diabolical plot. Like the Doctor, The Master has been played by several different actors throughout the series' run, going up against all the Doctors. He has a habit of disguising himself as other people, including those in powerful places and of kidnapping and other general evilness.