Among the classic authors of Swiss German literature are Jeremias Gotthelf (1797–1854) and Gottfried Keller (1819–1890). The undisputed giants of 20th-century Swiss literature are Max Frisch (1911–91) and Friedrich Dürrenmatt (1921–90), whose repertoire includes ''Die Physiker'' (The Physicists) and ''Das Versprechen'' (The Pledge), released in 2001 as a Hollywood film.