The Doctor (Doctor Who)
Jodie Whittaker took over the role as the Thirteenth Doctor in the 2017 Christmas special. In addition to the above-listed actors, others have played versions of the Doctor for the duration of particular storylines.
Notably, John Hurt guest starred as the War Doctor in the closing moments of the 2013 episode "The Name of the Doctor", the webcast "The Night of the Doctor" and the 50th Anniversary episode "The Day of the Doctor". The War Doctor is an incarnation existing between those of McGann and Eccleston. Hurt was never the programme's lead actor; his Doctor was retroactively inserted into continuity for the programme's 50th anniversary, and was written so as not to disturb the ordinal naming of the established Ninth, Tenth and Eleventh Doctors. In the 1986 serial "The Trial of a Time Lord", Michael Jayston played the Valeyard, an amalgamation of the Doctor's darker sides from between his twelfth and final incarnations.
Doctor Who
The Master is the Doctor's archenemy, a renegade Time Lord who desires to rule the universe. Conceived as "Professor Moriarty to the Doctor's Sherlock Holmes", the character first appeared in 1971. As with the Doctor, the role has been portrayed by several actors, since the Master is a Time Lord as well and able to regenerate; the first of these actors was Roger Delgado, who continued in the role until his death in 1973. The Master was briefly played by Peter Pratt and Geoffrey Beevers until Anthony Ainley took over and continued to play the character until Doctor Who's hiatus in 1989. The Master returned in the 1996 television movie of "Doctor Who", and was played by American actor Eric Roberts.