Antonio Salieri: Famous hater of the Mozart...if you believe the movie. Mozart actually did kvetch about Salieri's "trickery" in letters to his father and the two composers were unquestionably musical rivals.
Amadeus. Ironically a movie about another composer, but named after Mozart. I strongly suggest seeing the theatrical version, NOT the director's cut. At the beginning I was scandalized by Mozart, but by the end I liked him. Overall, my favorite character was the preacher, though. Also note that most of the details in the story aren't true.