Who is the Master, and how is he connected to the Doctor?

The Master is a recurring character in the British science fiction television series Doctor Who. He is a renegade Time Lord from the planet Gallifrey who is also a childhood friend and archenemy of the Doctor. Like the Doctor, the Master is able to regenerate into a new body when his current one is fatally damaged. This has allowed the character to be played by different actors throughout the series.

The Master's connection to the Doctor is complex and multifaceted. While the two are friends from their childhood on Gallifrey, they have become bitter enemies due to their opposing views on the universe and the role of the Time Lords. The Master sees himself as the yin to the Doctor's yang, and often seeks to prove himself as the superior Time Lord.

The Master has been a recurring character in Doctor Who since the early 1970s, and has been portrayed by several different actors over the years. Some of the most memorable portrayals of the character have been by Roger Delgado, Anthony Ainley, John Simm, and Michelle Gomez.