7. Perdita Weeks (Roslin Frey)
Roslin Frey isn't the most recognisable of Game of Thrones character names, and yet she's a central part of the show's biggest moment, because the Red Wedding just so happens to be her wedding.
The bride of Edmure Tully is played by Alexandra Dowling, but Perdita Weeks was the actress originally set to portray the character. Weeks turned down the part because she was set to film a mini-series called The Heretics, where she'd play a 13th Century villager. The show was supposed to film in Romania, but plans fell through, leading to Weeks attempting to get her part back. She told The Daily Mail:
"I gave up a role on Game Of Thrones to take the part and even rang the producers to beg for it back once I’d heard the news about Romania, but it was too late.’
The Heretics never happened, but it's not like Weeks has missed out on too much action: Dowling only appeared in The Rains of Castamere, and wasn't even mentioned again until Season 6, with almost no chance of returning now.