The Wolf Man (1941)

Starring Lon Chaney, Jr., Claude Rains, Warren William, Ralph Bellamy, Patric Knowles

Directed by George Waggner
(actor & director credits courtesy IMDB.com)

Young Larry Talbot returns home to manage his ancestral estate, where he tries to save a woman killed by a wolf, but after he's bitten, he soon begins to fear he could now be a werewolf.

Lon Chaney, Jr. stars in what became his most iconic role, that of the tortured Larry Talbot, cursed to transform into the bestial Wolf Man during the full moon.  It's a classic film, with a good cast of character actors, great foggy atmosphere, and a first-rate musical score.  Although Chaney would make scores more movies, he probably never got as terrific a showcase again, but went on to reprise the character in four more films.  There's some gaffes, with Chaney starting to transform into the Wolf Man in one set of clothes and then appearing in a completely different outfit as the monster, as well as the werewolf at the beginning of the film being played by an actual wolf rather than an actor.  But these are easily overlooked in this gem of a movie.