txtDefinition=Austrian composer (1732-1809) whose eighteenth-century fame eclipsed that of Mozart. Unlike Mozart, Haydn was a relatively late bloomer, composing most of his important music after the age of 35 (at which age Mozart was dead). Haydn played a seminal role in the development of the symphony and the {\uldb string quartet}{\v 154839}. His friendship with Mozart from ca. 1781 on was crucial to the musical development of both composers.