Since its first-time airing in 1963, there have been 12 different actors who assumed the title role of the Doctor in the sci-fi TV series.
The transition from one actor to another and the varied approach to the role that they bring is written into the plot of the show as regeneration into a new incarnation. It is a life process of the Time Lords through which the character of the Doctor takes on a new body and also new personality, which normally happens after sustaining injury which are often fatal to most other species.
Although each actor’s portrayal of the Doctor differs, they are all intended to be aspects of the same character and form part of the “Doctor Who” storyline.
The latest actor who is playing “Doctor Who” is Peter Capaldi. He has been doing it since last season. Before Peter, actor Matt Smith, played the role from 2010 to 2013.
The time-travelling nature of the plot of “Doctor Who” also meant that occasionally, story arcs involved different Doctors meeting each other similar to the time when Peter Capaldi and Matt Smith personally meet each other during the show’s 2013 Christmas special titled “The Time of the Doctor.”