Antonio Salieri (18 August 1750 – 7 May 1825) was an Italian composer and conductor from the Republic of Venice. As the Austrian imperial Kapellmeister from 1788 to 1824, he was one of the most important and famous musicians of his time, says Wikipedia.
In the 1780s while Mozart lived and worked in Vienna, he and his father Leopold wrote in their letters that several "cabals" of Italians led by Salieri were actively putting roadblocks in the way of Mozart's obtaining certain posts or staging his operas. There is evidence of Salieri's having engaged in such conspiratorial acts. At the beginning of the 19th century, increasing German nationalism led to a tendency to transfigure the Austrian Mozart's character, while the Venetian Salieri was given the role of his evil antagonist.[1] Carl Maria von Weber, a relative of Mozart by marriage[2] whom Wagner has characterized as the most German of German composers, is said to have refused to join Ludlams-Höhle, a social club of which Salieri was a member and avoided having anything to do with him.[3] These rumors then made their way into popular culture. Albert Lortzing's Singspiel Szenen aus Mozarts Leben LoWV28 (1832) uses the cliché of the jealous Salieri trying to hinder Mozart's career.
There is very little evidence of a contentious relationship between the two composers.