Famous as the force of nature that was Amy Pond, Scottish actress Karen Gillen actually made a brief previous appearance in Doctor Who, meaning that as well as Matt Smith, she's also been in an episode with David Tennant and Peter Capaldi. In The Fires of Pompeii, she plays one of the soothsayers of the Pyroville High Priestess. This was enough to put her on the radar for when Steven Moffat was looking for a new companion for Matt Smith and to do his bit to foster a coalition between the Doctor and the SNP. Little could fans have known from Gillen's brief part previously how she would come to dominate the series during the majority of the Matt Smith era.