1. Conleth Hill - Robert Baratheon
"Some doors close forever, others open in most unexpected places.” - Varys.
The most out-there entry on the list, it's almost unthinkable that the same actor who plays Varys could instead have worn the crown of King Robert Baratheon in Season 1.
Hill confirmed that he read for the part, only to leave the room and see that Mark Addy was in after him, and went away thinking "Well, he’d be all right for it."
And, of course, he was. Addy's Robert Baratheon is a highlight of Season 1, and among the best casting decisions the show has made. But so too is Hill as Varys, who it's fair to say got something of a sweeter deal: Bobby B lasted just seven episodes, while Varys is still going after seven seasons, although there was one kicker - he wasn't told until AFTER he'd accepted the part that he'd need to shave his head.
"A blessing, then."
Would you have liked to have seen any of these castings happen? Let us know down in the comments.