It's hard to say which view of Antonio Salieri is more firmly embedded: that he was the tormentor who drove Mozart to an early grave - perhaps even using a spot of arsenic just to make sure - or that he was a lousy composer. A few clunky numbers on the soundtrack of Amadeus, Milos Forman's 1984 film of Peter Shaffer's play, are all most of us will have heard of Salieri's music. Was there any more to him as a composer than that?

There are influential musicians who say that there was. Indeed, Salieri's operas have been undergoing a slow but steady exhumation. Next year the renovated La Scala in Milan is to reopen its doors with the work Salieri wrote for its very first performance back in 1778. And now Cecilia Bartoli has recorded an album devoted to his music. With an artist of Bartoli's clout on his side, it's safe to say that we're going to be hearing a lot more of Salieri the composer. And Salieri the poisoner? Sadly for those who like a good conspiracy theory, there's no evidence that he was any such thing. It's time to reappraise the man as well as his music.

If Salieri wasn't the enviously wrathful schemer of Forman's imagination, who was he? We have frustratingly little first-hand information. But the picture drawn by Volkmar Braunbehrens's 1989 biography is of a serious, steady, occasionally irascible man. There are, however, mentions of him as friendly and cheerful, and the Irish singer Michael Kelly, a good friend of Mozart, assures us that Salieri "would make a joke of anything". What is certain is that by 1781, when the 25-year-old Mozart set up home in Vienna, Salieri, six years his senior, was an established star.

Born in the northern Italian town of Legnano in 1750, he had been brought to Vienna aged 15, where he was introduced to his later mentor, Gluck, and to the emperor, Joseph II. Salieri was invited to join in chamber music sessions with the emperor, and soon found himself launched on a career in the imperial court. His appointment in 1774 as court composer and conductor of the Italian opera made him one of the most influential musicians in Europe.

An ambitious young composer such as Mozart could conceivably have wished Salieri out of the way, but the other way round? Hardly. So what if Mozart collaborated on Le Nozze di Figaro with Beaumarchais, the doyen of the Paris stage? Salieri was already working on Tarare, to a libretto by Beaumarchais himself, a work that would be a hit in Paris. And if Mozart's collaborations with the librettist Lorenzo da Ponte bore greater fruit than Salieri's? Well, no matter - it was Salieri, after all, who could claim credit for bringing Da Ponte to Vienna. True, after their first opera together flopped the composer swore he would rather have his fingers chopped off than work with him again, but he relented in time to write several that were far more successful.

However, if what Mozart's wife Constanze reported was true, there was one incident that might conceivably have sparked a rivalry. She claimed that Salieri had been offered Da Ponte's libretto for Cosi Fan Tutte - and had rejected it as being not worth setting. When Mozart got his hands on it, a humiliated Salieri had to eat his words.

Otherwise, though, any tensions between the two seem more like office politics. Salieri had to turn down the prestigious commission for La Clemenza di Tito, but had no real reason to resent Mozart for being the second choice. For his part, Mozart complains in letters to his father of being thwarted by Italian "cabals", but it often seems that he felt he had to make excuses to his grumpy, overambitious parent for any small failure. Far from blocking its performance, Salieri frequently conducted Mozart's work. And Mozart's death, as one respected musical journal wrote, was almost certainly caused not by poison but by "arduous work and fast living among ill-chosen company".

It was only after Mozart's demise that Salieri began to have any real reason to hate him. Unlike that of any before him, Mozart's music kept on being performed. Cut down at the peak of his powers - and with the added frisson of whispered rumours that he might have been murdered - he became the first composer whose cult of celebrity actually flourished after his death.

Salieri, however, had outlived his talent. He wrote almost no music for the last two decades of his life. Instead he spent time revising his previous works. He did have an impressive roster of pupils: Beethoven, Schubert, Meyerbeer and Liszt - not to mention Franz Xaver Mozart, his supposed adversary's young son. But the composer who had once been at the vanguard of new operatic ideas was not necessarily teaching his students to be similarly innovative; we can only be grateful that Schubert ignored his diatribes against the "intolerable" genre of Germanic lieder.

So how did this respected musician become the rumoured murderer of the great Mozart? Nobody knows for certain. But in his final weeks Mozart is reported to have believed he had been poisoned, and had gone so far as to blame hostile Italian factions at the Viennese court. People put two and two together and pointed the finger at Salieri. And who could resist a story this good? Certainly not his fellow composers. There are mentions of it in Beethoven's Conversation Books. Weber, Mozart's father-in-law, had heard it by 1803, and cold-shouldered Salieri ever after. And 20 years later it was still doing the rounds; Rossini joked about it when he met Salieri in 1822.

As the rumour gathered strength, all denials only served to reinforce it. Then, in 1823, Salieri - hospitalised, terminally ill and deranged - is said to have accused himself of poisoning Mozart. In more lucid moments he took it back. But the damage was done. Even if few believed the ramblings of a confused old man, the fact that Salieri had "confessed" to Mozart's murder gave the rumour some semblance of validity.

Today, although we know it's almost certainly false, the image of Salieri as poisoner persists. It's largely because so many artists have been drawn to it - and their responses can reveal more about themselves than about the story. Pushkin, who wrote his Little Tragedy on the subject just five years after Salieri's death, made him unambiguously a murderer. But still, there's a sense of identification with both the deep-thinking Salieri and the light-hearted Mozart. Rimsky-Korsakov, writing about it 67 years later, mostly imitated classical styles, except when Mozart plays something Salieri hails as "genius" - which is where, funnily enough, we get our only real taste of pure Rimsky.

And then, of course, there's Amadeus. The success of the film has done more than anything to promote the image of Salieri as malefactor, even though the play on which it is based rests on the fact that he wasn't actually a murderer. But in identifying with Salieri, Shaffer has made the composer's little tragedy into something far, far bigger: something that holds up a mirror to a side of human nature we'd rather not confront.

All these works, though, miss out one important point: that Shaffer's "patron saint of mediocrities" wrote some fine music. It's true that his output is inconsistent, that he rarely reaches the same heights Mozart scaled. But, equally, some of it is original and inventive - and the best is very good indeed. Salieri may have made a great cinematic villain, but perhaps in the future we can remember him for something he actually did.

· Cecilia Bartoli performs Salieri arias with the Orchestra of the Age of Enlightenment at the Barbican, London EC2. Box office: 0845 120 7500. Cecilia Bartoli: The Salieri Album is out on Decca.