Having famously played a genie and a nanny before, it turns out Robin Williams also wanted to add "half-giant gamekeeper" to his filmography. Yep, the beloved actor really wanted to get involved in the Harry Potter film universe when it was originally launched in 2001 by playing Rubeus Hagrid -- but a very specific casting rule prevented him from journeying to Hogwarts.
As casting director Janet Hirshenson revealed to Huffington Post that the "Harry Potter" film producers imposed a "Brits only" rule for the film's principle cast members, which included Hagrid. Because of that, the American Williams was turned down for the part of Hagrid, even though he had called up director Chris Columbus and asked to play the part.
“Robin [Williams] had called [director Chris Columbus] because he really wanted to be in the movie, but it was a British-only edict, and once he said no to Robin, he wasn’t going to say yes to anybody else, that’s for sure,” said Hirshenson. “It couldn’t be.”
The part ended up going to Robbie Coltrane, who was apparently also J.K. Rowling’s first choice for the part.
The Guardian also found a quote from Williams in 2001, where he alluded to this development without specifically naming the "Harry Potter" franchise. “There were a couple of parts I would have wanted to play, but there was a ban on [using] American actors.”
Williams passed away in August 2014.