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".
John Simm
In 2007, Simm was chosen by Russell T. Davies to play The Master, the nemesis of The Doctor in the long-running BBC series "Doctor Who". He appeared in the final three episodes of series three: "Utopia", "The Sound of Drums", and "Last of the Time Lords". When originally cast in the third series of Doctor Who, it was announced that he would be playing a character by the name of Mr Saxon, a name that was later revealed as an alias of the character he was portraying. He reprised the role in the 2009 two-part special "The End of Time". In 2008, Simm played Edward Sexby in "The Devil's Whore", a four-part English Civil War epic for Channel 4. He performed at the Royal Variety Performance with Alexander Armstrong and Ben Miller, and starred in the film "Skellig", broadcast on Sky1 in April 2009.