8. Robin Williams - Hagrid (Harry Potter)
Do you know the reason why there are no American actors in any of the Harry Potter movies? This is the reason why. This is the reason why J.K. Rowling included a clause in her contract with Warner Bros. regarding the casting of any actors that weren't British, and why American castings totally weren't going to happen: because they originally tried to get Robin Williams in the part of gentle giant Hagrid, which - you'll agree - would have been truly terrible. Yes, back when Harry Potter was still a thing you might not have heard of yet, Warner Bros. had their hearts set on Williams - best-known for both dramatic and comedy roles at this time, and familiar with both kids movies and kids movies featuring lots of CGI, given a recent turn in
Jumanji - as the guy who should play Hagrid in the first movie adaptation. Rowling, presumably disturbed by this notion, nipped it in the bud before it was too late. Nice one, J.K..