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".
Colin Baker
At the time of Baker's casting as Davison's successor, he was the only actor portraying the Doctor to have appeared in the television series as another character prior to taking on the leading role (in 2013 Peter Capaldi was announced as the Twelfth Doctor after having previously appeared in another role in the 2008 episode "The Fires of Pompeii"). When Baker was cast to replace Davison, many fans cited that shooting scene in "Arc of Infinity", prompting Baker to say jokingly that he got the part of the Doctor by killing the incumbent. He is no relation to Tom Baker, who previously played the Fourth Doctor in "Doctor Who".