The Master (Doctor Who) performer Sacha Dhawan
The Master, or "Missy" in their female incarnation, is a recurring character in the British science fiction television series Doctor Who and its associated spin-off works. They are a renegade alien Time Lord and the childhood friend and later archenemy of the title character, the Doctor. They were most recently portrayed by Sacha Dhawan. 
Multiple actors have played the Master since the character's introduction in 1971. Within the show's narrative, the change in actors and subsequent change of the character's appearance is sometimes explained as the Master taking possession of other characters' bodies or as a consequence of regeneration, which is a biological attribute that allows Time Lords to survive fatal injuries or old age.
The Master was originally played by Roger Delgado from 1971 until his death in 1973. The role was subsequently played by Peter Pratt, Geoffrey Beevers, and Anthony Ainley, with Ainley reprising the role regularly through the 1980s until the series’s cancellation  in 1989. Eric Roberts took on the role for the 1996 Doctor Who TV film. Since the show's revival in 2005, the Master has been portrayed by Derek Jacobi, John Simm, Michelle Gomez, and Sacha Dhawan.
Beevers, Roberts, Jacobi, Simm, and Gomez have reprised the role in audio dramas produced by Big Finish Productions. At the same time, Alex Macqueen, Gina McKee, Mark Gatiss, James Dreyfus, and Milo Parker portrayed incarnations unique to Big Finish.