Carl Czerny
He was a personal friend and patron of the Viennese composers Ludwig van Beethoven, Franz Schubert and his cousins, the playwright Franz Grillparzer (1791–1872), and Carl Czerny. Schubert dedicated his musical setting of Grillparzer's Serenade "Hesitantly Quiet" (D921) to Sonnleithner's wife Louise. And it was Sonnleithner who handled Carl Czerny's will.