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".
David Tennant
"Doctor Who" returned to British screens in 2005, with Christopher Eccleston playing the role of the Ninth Doctor in the first series. Tennant replaced him as of the second series, making his first, brief appearance as the Tenth Doctor in the episode "The Parting of the Ways" (2005) at the end of the regeneration scene, and also appeared in a special shown as part of the 2005 Children in Need appeal, broadcast on 18 November 2005. He began filming the new series of "Doctor Who" in late July 2005. His first full-length outing as the Doctor was a 60-minute special, "The Christmas Invasion", first broadcast on Christmas Day 2005. Tennant had been formally offered the role of the Doctor during rehearsals for "The Quatermass Experiment". Although the casting was not officially announced until later in April, both castmates and crew became aware of the speculation surrounding Tennant; in the live broadcast Jason Flemyng (Quatermass) changed his first line to Tennant's Dr Briscoe from "Good to have you back, Gordon" to "Good to have you back, "Doctor"" as a deliberate reference.