Doctor Who
Thirteen actors have headlined the series as the Doctor. The transition from one actor to another is written into the plot of the show with the concept of regeneration into a new incarnation, a plot device in which a Time Lord "transforms" into a new body when the current one is too badly harmed to heal normally. Each actor's portrayal is unique, but all represent stages in the life of the same character. Together, they form a single lifetime with a single narrative. The time-travelling feature of the plot means that different incarnations of the Doctor occasionally meet. The Doctor is currently portrayed by Jodie Whittaker, who took on the role after Peter Capaldi's exit in the 2017 Christmas special "Twice Upon a Time".
The Doctor (Doctor Who)
John Hurt plays a mysterious past incarnation of the Doctor in the 50th anniversary special "The Day of the Doctor", with minor roles in "The Name of the Doctor" and mini-episode "The Night of the Doctor", created as a "mayfly Doctor" by Steven Moffat. In the television episodes, he is credited as "The Doctor", but he is introduced as "The War Doctor" in "The Night of the Doctor". The end of "The Name of the Doctor" closes with text superimposed over footage of Hurt introducing him, pictured to the left, which was unprecedented for the show. In "The Day of the Doctor", Hurt appears in a "multi-Doctor" special alongside Matt Smith and David Tennant as the Eleventh and Tenth Doctors, respectively. The three are collectively credited as "The Doctor" alongside Christopher Eccleston, Paul McGann, Sylvester McCoy, Colin Baker, Peter Davison, Tom Baker, Jon Pertwee, Patrick Troughton and William Hartnell, although the latter nine appeared only through the reuse of archive footage. Tom Baker did reappear, but as "the Curator", an ambiguously different character who he was not credited for playing. A voice actor, John Guilor, recorded a line of audio impersonating the First Doctor, for which he was credited as "Voice Over Artist".