8. David Tennant
OK, so David
was in Doctor Who, and in a very big role indeed, as it turns out. Before he stepped aboard the TARDIS as the beloved Tenth Doctor, though, he was originally lined up to guest star as Gabriel Sneed, the undertaker, in Series 1's Dickensian classic The Unquiet Dead. The role was ultimately given to Alan David, of course, when it was decided by the episode's writer, Mark Gatiss, that the character should be older. It's interesting, though, to think that David came close to joining the coveted rank of Doctor Who actors who were reinstated into the Whoniverse in a new role after an initial guest appearance. With the likes of Freema Agyeman, Karen Gillan and Peter Capaldi in the same coveted club, he certainly would've been in good company. A role in The Unquiet Dead would've seen David sharing the screen with his future predecessor, too, which is always fun. There's still a chance to see Christopher Eccleston and David Tennant together, though, as they both appear in the 1996 movie June which starred the former as its protagantist and the latter as... erm, a Drunken Undergraduate. Because everyone's gotta start somewhere, right?