When Matt Smith quit his role as Doctor Who, showrunner Steven Moffat and his team had to go in search of a new star, before deciding on Peter Capaldi. Steven has now spoken about having Peter as the new Doctor Who, praising the actor as already being a national treasure.

Peter Capaldi is the new Doctor Who
Moffat told Broadcast, "Peter's already a bit of a national treasure. As most people have realised, the moment you think of him in the part, you find it hard to think of anyone else. Every time I was at a TV do and Peter was there, he'd come over to talk about Doctor Who and he was the first to congratulate Matt. I started thinking - what if that genius actor might actually say 'yes'?"
Steven also spoke about replacing Matt Smith with Peter Capaldi, adding, "I sympathise with the kids who've grown up with Matt Smith. It's like when you move home and your mum and dad say, 'You'll make new friends'. I always resented the intruder but then after a while, I forgot there had been one before him."

Matt Smith is leaving the show
Matt Smith will star in the Doctor Who 50 Anniversary Special, before then leaving the role in the Doctor Who Christmas Special, where he will then hand over to Peter Capaldi. The Doctor Who 50th Anniversary Special will air worldwide on Saturday, November 23.
Peter Capaldi is Doctor Who