Game of Thrones has an unaired pilot out there that has somehow never seen the light of day. In it, Daenerys Targaryen was originally played by Tamzin Merchant (left), Jamie Campbell Bower was Waymar Royce, and Jennifer Ehle was Catelyn Stark.
The two female characters were eventually, of course, played by Emilia Clarke and Michelle Fairley, respectively. Waymar was played by Rob Ostlere for one episode (Waymar is killed by White Walkers).
Pilot recasting is not uncommon, for a variety of reasons; sometimes creators decide to go in a different direction with a character or, as was the case with Bower, the actor is unavailable for reshoots. In Ehle's case, she felt it was too soon after the birth of her daughter to commit to such a massive project, so she chose to leave Game of Thrones voluntarily.
