Karlheinz Stockhausen (August 22, 1928 - December 5, 2007) was a German composer, widely acknowledged by critics as one of the most important but also controversial composers of the 20th and early 21st centuries. He is known for his ground-breaking work in electronic music, aleatory (controlled chance) in serial composition, and musical spatialization. He was educated at the Hochschule für Musik Köln and the University of Cologne, and later studied with Olivier Messiaen in Paris, and with Werner Meyer-Eppler at the University of Bonn.