Mozart and Salieri
Like everyone who grew up in the 80s, my perceptions of musical history are greatly skewed by this excellent movie, based, in turn, on Peter Shaffer's highly successful play. Everyone knows the premise: Antonio Salieri drives himself to suicide (attempted and failed) over his obsession with the idea that God is taunting him through Mozart. Indeed, he believes he has poisoned Mozart to death out of jealousy. Though I always wondered if the main point of the play, really, wasn't to have been highlighting what a boor the real Mozart was - in contrast to his apollonian music.
To the extent that the play is meant to have a bit of fun at the expense of the prim churchgoers who idolize Mozart, I suppose it's only fitting that someone should have come out with an internet quiz testing the listener's ability to distinguish between Mozart and Salieri compositions. The link goes to just that - and I'm ashamed to say I scored barely above chance (6/10) - missing even the passage from Don Giovanni. So Shaffer gets a well-deserved laugh at my expense, I suppose.
Reality seems to have been that there was some minor rivalry between Mozart and Salieri. Their respective positions in society as portrayed in the film are accurate - but the lengths to which Salieri went to discredit Mozart might not be. Rumors that Salieri blamed himself for Mozart's early death are real, but the substance behind them apparently not so much (all of the witnesses to this supposed deathbed confession - converted in the movie to a suicide attempt - denied having heard it when questioned). In fact, Salieri seems to have largely given Mozart his due in public, even promoting some of his operas and masses.
As for where the perception Shaffer's play is based on came from - it's Pushkin's fault.