David WalliamsDavid Walliams was considered for the role of Barty Crouch Jr.
At least one full-scale dragon was constructed on set, which could even blow real fire.
John WilliamsJohn Williams passed on scoring this movie in favor of Memoirs of a Geisha.
Safety divers swam in with scuba regulators to allow them to breathe without having to surface. These scenes were shot in a huge purpose-built tank with a blue-screen background. Daniel RadcliffeDaniel Radcliffe alone logged around 41 hours 38 minutes underwater during the course of filming. At one point during training he inadvertently signaled that he was drowning, sending the crew into a huge panic to bring him back up to surface.
Mike NewellMike Newell decided against the studio's original idea of adapting the extremely long book into two separate films to be released several months apart, figuring that he could cut enough of the book's bulky subplots to make a workable film. It was Alfonso CuarónAlfonso Cuarón, the director of Harry Potter and the Prisoner of Azkaban, who convinced him.
Katie LeungKatie Leung hadn't intended to audition for the role of Cho Chang. Her father had told her where the audition was being held and she decided to go before her shopping trip.
Stanislav IanevskiStanislav Ianevski, who plays Viktor Krum, has only two lines in the entire film totaling 20 words.
Ralph FiennesRalph Fiennes was not wearing any make up to cover his nose. In order to make the character scarier, film editors digitally removed it. Also, the "red, snake-like eyes" the novel describes were not added, due to the actor's thought that the expression in his eyes would provide a better idea of Lord Voldemort's insanity and malignity.