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
In October 2015, Big Finish Productions announced that Tennant would return to the role of the Tenth Doctor alongside Catherine Tate as his former companion Donna Noble in three new stories from Big Finish. The stories feature current and previous Doctor Who actors, including Strax actor Dan Starkey, former Davros actor Terry Molloy, and many veterans of Big Finish, including Niky Wardley, who portrayed Eighth Doctor companion Tamsin. The three stories were released in May 2016.