Note the ways in which the Mozart-Salieri relationship changes.

English playwright Peter Shaffer's 1979 play Amadeus is a tale of the life of composer Wolfgang Amadeus Mozart. Later remade into a feature film, it focuses on an embellished and fictionalized account of the relationship between Mozart and Italian composer Antonio Salieri.
Salieri, who is Mozart's senior, has heard of the younger composer since his early reputation as a musical prodigy spread throughout Europe. When Salieri is finally introduced to Mozart, however, he becomes disillusioned at what he perceives as Mozart's crass behavior.
Salieri spends much of the rest of the play as Mozart's passive aggressive rival, feigning support for Mozart while using his influence as imperial court composer to secretly sabotage his career behind the scenes. Mozart is oblivious to Salieri's machinations, expressing gratitude for his overt efforts.
Toward the end of the play, Salieri becomes conflicted about his own plans to destroy Mozart and his increasing affection for the composer's works. Nonetheless, he induces Mozart to transcribe the rituals of Freemasonry into an opera—The Magic Flute—which meets with the disapproval of prominent Masons in Vienna. Thus begins the end of Mozart and Salieri's relationship, with Salieri, it is strongly suggested, murdering Mozart.
Ultimately, the conflict between Salieri's two visions of Mozart drives the Italian mad.
http://dramatica.com/analysis/amadeus