10 Actors With Multiple Roles In Doctor Who
3. Peter Capaldi
First Role: Caecilius (The Fires of Pompeii)
Second Role: The Twelfth Doctor (The Time of the Doctor - Twice Upon A Time)
One of the only actors to appear in Doctor Who before going on to snag the title role, Peter Capaldi's first acting contribution to the show came in 2008's The Fires of Pompeii, opposite David Tennant as the Doctor and Catherine Tate as Donna Noble.
Capaldi played Caecilius, one of the few people that the Doctor chose to rescue from the eruption of Mount Vesuvius. He was then cast as the Twelfth Doctor, taking over from Matt Smith at the end of the 2013 Christmas special, The Time of the Doctor.
Interestingly - and unlike a lot of the other examples on this list - an explanation was actually given for why Caecilius looks exactly like the Twelfth Doctor, despite the two being totally different characters. In Series 9's The Girl Who Died, the Twelfth Doctor realises that he resembles Caecilius because it's a reminder that he should always try and save people, no matter the circumstances or consequences.
In addition, Capaldi also has a third role in the Whoniverse. He played John Frobisher in 2009's Torchwood: Children of Earth, a character who - according to Steven Moffat - is actually a descendant of Caecilius. This means that Frobisher's death was a way for time to "correct" itself: this particular bloodline was supposed to end with Caecilius, but it didn't, so the universe ended it with Frobisher instead.