Daniel Radcliffe as Harry Potter: the main protagonist. Now entering his fourth year as Hogwarts, Harry is unknowingly entered into the Triwizard tournament.
Rupert Grint as Ron Weasley: one of Harry's best friends. Although he falls out with Harry at the beginning of the Triwizard tournament, the pair reconcile and remain good friends.
Emma Watson as Hermione Granger: one of Harry's best friends. Although she loathes her position as an intermediary between Harry and Ron during their period of hostility, she remains supportive of Harry throughout.
Ralph Fiennes as Lord Voldemort: the primary villain. The darkest wizard of age, who returns to a human body at the climax of the film.
Michael Gambon as Albus Dumbledore: the Hogwarts headmaster. He is supportive of Harry throughout the year, although he does not suspect Moody until it is almost too late.
Brendan Gleeson as Alastor Moody: the Defence Against the Dark Arts teacher. The real Moody is not seen until the end of the film.
Robert Pattinson as Cedric Diggory: a rather dishy Hogwarts student who is chosen as a Triwizard champion. He is murdered by Voldemort in the graveyard at the end of the film.