Carey Mulligan will forever hold a place in Doctor Who history for playing Sally Sparrow in the episode "Blink," one of the best episodes of Doctor Who of all time, but she could have had a much bigger role in the venerable franchise.
"Blink" was written by Steven Moffat, based on a short Doctor Who comic he wrote. Moffat would later go on to become Doctor Who showrunner while Mulligan went on to Hollywood. Moffat reflected on the episode in an interview with Radio Times.
"Oh my God, Carey Mulligan!" he says. "It's funny but 'Blink,' I say immodestly, is a very famous episode of television and yet Carey Mulligan, who was the star of it, I'm almost certain wouldn't even remember being in Doctor Who. I don't think she was much of a fan or anything. They liked her so much, they said, 'Do you want to be the next companion?' but she said no. God, she was amazing."
That's right, it was nearly Carey Mulligan who replaced Freeya Agyeman Martha Jones in the fourth series of Doctor Who instead of Catherine Tate's Donna Noble, but Mulligan said no and Moffat never tried to reel her back onto the series because he knew she wouldn't agree. However, Moffat wonders if Mulligan only appearing in that one episode is part of what made Sally Sparrow's story so special.
"But then does that character become more special because you never see her again?" he wonders. "She just passes through the Doctor's life. It's surprising the people who do love being part of it. John Hurt loved being the Doctor and was quite insistent, asking, 'Am I a real Doctor? Do I really count?' And we said, 'Yes, you count. You're on the poster. It is definitely you.' David Bradley is so thrilled that he is really the Doctor now. Because obviously, he was sort of the Doctor in An Adventure in Space and Time. He's been a star forever, but being the Doctor is special, somehow. He's a bit like Hartnell in a way. He's got a mean face but he's the nicest man alive, so sweet and generous."
Moffat's final episode of Doctor Who, the Doctor Who Christmas Special "Twice Upon a Time," will air Christmas Day on BBC One and BBC America.