Joseph Sonnleithner

Joseph Ferdinand Sonnleithner (3 March 1766 – 26 December 1835) was an Austrian court agent, councillor, librettist, theater director, and archivist. He was the son of Christoph Sonnleithner, brother of Ignaz von Sonnleithner and uncle of Franz Grillparzer and Leopold von Sonnleithner. He was a personal friend of Ludwig van Beethoven, and he wrote numerous librettos, among them, Beethoven's stage opera ''Fidelio'', ''Faniska'' by Luigi Cherubini and ''Agnes Sorel'' by Adalbert Gyrowetz. Provided by Wikipedia