King Crimson is a progressive rock group from England formed in 1969 by guitarist Robert Fripp and drummer Michael Giles. Though originally an all-British musical group, later members have included a number of Americans, most notably Adrian Belew, and Tony Levin. The name "King Crimson" was coined by Peter Sinfield as a synonym for Beelzebub, prince of demons.

King Crimson's debut album was In the Court of the Crimson King. The first major success of the new genre of progressive rock, many bands that would come to dominate 'prog' in the 1970s first sought to emulate In the Court of the Crimson King, including Genesis, The Alan Parsons Project, and later Rush.

The lineup of King Crimson has at times changed drastically from album to album. Original lead singer and bassist Greg Lake left the group - as did lyricist Peter Sinfield - and went on to fame with Emerson, Lake & Palmer in 1970, replaced by Gordon Haskell, Boz Burrell, and, briefly, Jon Anderson of Yes. Also from Yes came drummer Bill Bruford, who joined King Crimson in 1972 and became one of the more enduring members. For the next three years, Bruford and Fripp were joined by future Asia frontman John Wetton. With comparatively few additional musicians, these mid-1970s albums and performances showed a more raw and stylistically focused - though still improvisational - King Crimson. In 1974 the band split temporarily.

In 1981, bassist Tony Levin and guitarist/singer Adrian Belew joined Fripp and Bruford in a band initially called Discipline. Changing the name back to King Crimson, the four released a trio of studio albums which preserved the classic heavy and improvisational sound, but also embraced 1980s musical influences and technologies.

In 1984 the band split up again, then re-formed in 1994 with former Mr. Mister drummer Pat Mastelotto joining forces with and later replacing Bruford. This lineup included bassist Trey Gunn - playing warr guitar and chapman stick - forming a "double trio" of two guitarists, two bassists and two drummers. In between KC commitments, various combinations of the members convened in different "ProjeKcts": ProjeKct One, ProjeKct Two, ProjeKct Three, ProjeKct Four, and ProjeKct X, with Robert Fripp describing them as "fraKctals" of the band with the purpose of "research and development".

2000-2003 saw a new incarnation of King Crimson, without Bruford and Levin, which culminated in the album The Power to Believe and a concert tour. Trey Gunn left the group afterwards, but Fripp and Belew announced that they would meet in 2007 and think about future KC music. Tony Levin agreed to replace Gunn on bass/stick.

A new King Crimson line-up was announced in late 2007 and scheduled for rehearsals in 2008, consisting of Fripp, Belew, Mastelotto, Levin, and Gavin Harrison of Porcupine Tree. In August 2008 the band set out on a brief four-city tour in preparation for King Crimson's fortieth anniversary in 2009. A short time thereafter, on 20th August 2008, DGMLive (a web medium for Fripp to release live recordings) issued a download-only release of the August 7th, 2008 concert in Chicago. The show reveals a drum-centred direction but the set list, consistent with the rest of the tour, contains no new material or extended improvisation. However, many of the pieces from the back catalogue receive new arrangements, most notably the renditions of "Neurotica," "Sleepless", and "Level Five", all of which are given percussion-heavy overhauls, presumably to highlight the return to the dual-drummer format. More recordings from the New York shows are scheduled for download soon as well. There has been talk of more King Crimson shows in 2009, but nothing definite has arisen yet.

In 2008, Steven Wilson began remixing the studio catalogue into 5.1 Surround Sound for possible future release.

Despite its many changes, King Crimson has retained a consistent sound and atmosphere, largely as a result of Fripp's signature guitar work. Though they have not had a commercial success since their first album, the band has one of the most devoted followings of any musical group. Their live albums outnumber studio albums by a wide margin (some of them being "official" bootlegs), and there are more than enough ex-members to fully staff the 'classic' KC revival group known as 21st Century Schizoid Band.

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