1. Gillian Anderson
While an X-Files/Doctor Who crossover will probably never happen (and would fail to live up to the hype even if it did), it would still be great to see Gillian Anderson take a role in the show, and if certain rumours are to be believed,
she very almost did. After all, she's another sci-fi icon who would create additional interest in an episode and her appearance would allow the writers to make some of those formidable in-jokes they seemingly love so much, too. That wouldn't be the main reason to cast her, though. She's a really good actor, able to play from down to eath and forceful to completely ethereal (just see her Miss Havisham in the BBC's Great Expectations for the latter). She could be either a fearsome opponent or even a fearsome ally for Twelve and Clara. Just imagine the sparks flying if the Doctor landed on an alien planet where Anderson's character was in charge and didn't like the look of the newcomer. It'd be positively electrifying for all concerned. What's more, she's been doing a lot of BBC work in recent years with the aforementioned Great Expectations adaptation and playing the lead role in The Fall. This may mean she's open to working on Who and she can could with the fandom, too, thanks to many years of interacting with X-Files fans. Admittedly, she may have a busy schedule lined up. There's potentially a third series of The Fall to come as well as a bigger role in Hannibal and maybe even an X-Files revival. If she could find the time, however, the producers would be silly not to sign her up.
What did you think of this list? Are there any other actors who should guest star in Series 9? Share your own suggestions in the comments section below.