9. Liam Burke
The first of the actors on the list whom you're unlikely to have heard of - Liam Burke appeared as Mr. Boaz back in 2008's City of Ember. However, he was also set to appear as the Mad King, Aerys Targaryn II, back in Season One of Game of Thrones. Apparently scenes were filmed of Robert Baratheon's Rebellion, which took place more than twenty years before the events of the series and in which we would have witnessed the death of Ned Stark's brother and father in the court of the Mad King. The decision was made, for the sake of time and simplicity to remove these flashback sequences - the plot of Game of Thrones is sprawling enough without resorting to non-linear storytelling. Still, it would have been fascinating to witness the acts of a tyrant that served to make Robert king, Ned Stark his subject, and Jaime Lannister into the infamous Kingslayer.