Some of his patrons, including Prince Lobkowitz and Prince Lichnovsky, gave him annual stipends in addition to commissioning works and purchasing published works. Perhaps his most important aristocratic patron was Archduke Rudolf of Austria, the youngest son of Emperor Leopold II, who began studying piano and composition with him. This led to a friendship that lasted continuously until 1824. Beethoven dedicated 14 compositions to Rudolf, including some of his most important works - the Archduke Trio, Op. 97 and Missa Solemnis op. 123.