Long before stepping aboard the TARDIS as Amy Pond, Karen Gillan left a somewhat less promiment mark on the Doctor Who mythology. OK, so it wasn't that long before, since she was revealed as the new companion just over a year later, but her Doctor Who debut actually came during David Tennant's era which already feels like it was a lifetime ago (unless you're the Doctor, of course, in which case it was two lifetimes ago!). The actress appeared in the Series 4 episode The Fires of Pompeii as a Soothsayer and she's in good company when it comes to guest stars who were reinstated in a leading role. She followed in the formidable footsteps of Colin Baker - who played Commander Maxil in Arc of Infinity (1976) before being cast as the Sixth Doctor - and Freema Agyeman, who appeared as Adeola in Series 2's Army of Ghosts (2006) before she was killed by a Cyberman and returned as Martha Jones three episodes later. Let's not forget Peter Capaldi, of course, who encountered the Tenth Doctor as Caecilius, also in The Fires of Pompeii, before taking over the mantle as the show's leading Time Lord himself for Series 8. As a bonus tidbit of trivia, the process of casting the new TARDIS co-resident is always shrouded in secrecy and Karen's auditions were given the code word of 'Panic Moon' - an anagram of 'companion' - to avoid any scrutiny. It's a shame the show can't invest as much effort into protecting their upcoming storylines. Boom.
Dan Butler is the Doctor Who Editor at WhatCulture.com. When he isn't writing his own articles or editing other people's, he can be found trawling the internet for gifs of Steven Moffat laughing. Contact him via dan.butler@whatculture.co.uk.