Karlheinz Stockhausen (; 22 August 1928 – 5 December 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. Another critic calls him "one of the great visionaries of 20th-century music" . He is known for his groundbreaking work in electronic music, aleatory (controlled chance) in serial composition, and musical spatialization.