Master (Doctor Who)

The Master is a powerful supervillain from the Doctor Who series of television shows, movies, cartoons and comic books - he is an insane, evil member of the Time Lords, making him in many ways an evil twin of the Doctor despite them not being biologically related.

While almost all of the Doctor's incarnations are shown as brilliant yet heroic defenders of humanity and the time-stream all of the Master's incarnations are criminal masterminds who hate humanity and are quite happy to cause chaos across time and space to achieve their goals.

The Master is also deeply megalomaniacal and shows signs of psychopathic behaviour as his greatest fear in the universe is being outdone by the Doctor - leading him to becoming obsessed with ruining everything the Doctor stands for.. this has served to make the Master one of the Doctor's greatest and most reoccuring opponents and also the one that has caused the most emotional pain to the Doctor during the decades long feud between the two characters.

Keeping with the "evil twin" idea the Master has taken on multiple forms, just as the Doctor has, his most recent form is portrayed by John Simm - who played the insane Time Lord in both the "Drums Of War" and "The End Of Time".