10. Scott Bakula

Over its long history, Doctor Who has featured many famous faces. John Cleese, Brian Blessed, Derek Jacobi, Kylie Minogue, Claire Bloom and Michael Gambon have all put in guest appearances, among many others. On occasion, celebrities have also lent their voice to an episode. They include Brian Cox, Michael Sheen, Imelda Staunton and most recently Ian McKellen. And every so often, Doctor Who can serve as the springboard for young talent. Carey Mulligan got her big break with her own starring role in 2007s Blink. But there is also a plethora of stars that were considered for guest parts but who for one reason or another did not appear. Here are ten of them.Best known as the time-travelling Dr. Sam Beckett from Quantum Leap and Captain Jonathan Archer from Star Trek: Enterprise, Scott Bakula is no stranger to sci-fi. So its not surprising that he was once considered for a role in Doctor Who. He was offered the part of Isaac, the noble sheriff in this season's episode A Town Called Mercy. At a Star Trek convention, Bakula explained that he is a fan of the show and wanted the part but the filming dates clashed with other commitments. The role ultimately went to Farscape and Stargate SG-1 star Ben Browder. It would have been interesting to see the Doctor come face to face with Sam Beckett. Of course, it might have been somewhat awkward given that Doctor can go anywhere in time and space and Beckett is limited to his own lifespan. Is there such a thing as time travel envy?