Karlheinz Stockhausen (German: [kaRl'haInts 'StokhaUzn]; 22 August 1928 - 5 December 2007) was a German composer, widely acknowledged by critics as one of the most important (Barrett 1988, 45; Harvey 1975b, 705; Hopkins 1972, 33; Klein 1968, 117) but also controversial (Power 1990, 30) composers of the 20th and early 21st centuries. A critic calls him "one of the great visionaries of 20th-century music" (Hewett 2007). He is known for his groundbreaking work in electronic music, for introducing controlled chance (aleatory techniques or aleatoric musical techniques) into serial composition, and for musical spatialization.

Stockhausen, along with John Cage, is one of the few avant-garde composers to have succeeded in penetrating the popular consciousness (Anon. 2007b; Broyles 2004; Hewett 2007). The Beatles included his face on the cover of Sgt. Pepper's Lonely Hearts Club Band (Guy and Llewelyn-Jones 2004, 111). This reflects his influence on the band's own avant-garde experiments as well as the general fame and notoriety he had achieved by that time (1967). In particular, "A Day in the Life" (1967) and "Revolution 9" (1968) were influenced by Stockhausen's electronic music (Aldgate, Chapman, and Marwick 2000, 146; MacDonald 1995, 233-34). Stockhausen's name, and the perceived strangeness and supposed unlistenability of his music, was even a punchline in cartoons, as documented on a page on the official Stockhausen web site (Stockhausen Cartoons). Perhaps the most caustic remark about Stockhausen was attributed to Sir Thomas Beecham. Asked "Have you heard any Stockhausen?", he is alleged to have replied, "No, but I believe I have trodden in some" (Lebrecht 1985, 334, annotated on 366: "Apocryphal; source unknown").  Stockhausen's fame is also reflected in works of literature. For example, he is mentioned in Philip K. Dick's 1974 novel Flow My Tears, the Policeman Said (Dick 1993, 101) and in Thomas Pynchon's 1966 novel The Crying of Lot 49. The Pynchon novel features "The Scope", a bar with "a strict electronic music policy". Protagonist Oedipa Maas asks "a hip graybeard" about a "sudden chorus of whoops and yibbles" coming out of "a kind of jukebox." He replies, "That's by Stockhausen... the early crowd tends to dig your Radio Cologne sound. Later on we really swing" (Pynchon 1999, 34).  The French writer Michel Butor acknowledges that Stockhausen's music "taught me a lot", mentioning in particular the electronic works Gesang der Junglinge and Hymnen (Santschi 1982, 204).  Later in his life, Stockhausen was portrayed by at least one journalist, John O'Mahony of the Guardian newspaper, as an eccentric, for example being alleged to live an effectively polygamous lifestyle with two women, to whom O'Mahony referred as his "wives", while at the same time stating he was not married to either of them (O'Mahony 2001). In the same article, O'Mahony claims Stockhausen said he was born on a planet orbiting the star Sirius. In the German newspaper Die Zeit, Stockhausen stated that he was educated at Sirius (see Controversy below).

Did he influence any other muscians