King Crimson were an English-based progressive rock band formed in London in 1968. Led by guitarist Robert Fripp, they drew inspiration from a wide variety of music, incorporating elements of classical, jazz, folk, heavy metal, gamelan, blues, industrial, electronic, experimental music and new wave. They exerted a strong influence on the early 1970s progressive rock movement, including on contemporaries such as Yes and Genesis, and continue to inspire subsequent generations of artists across multiple genres. The band has earned a large cult following, especially in the 21st century.

Founded by Fripp, Michael Giles, Greg Lake, Ian McDonald and Peter Sinfield, the band's debut album, In the Court of the Crimson King (1969), remains their most commercially successful and influential release. The next two albums, In the Wake of Poseidon and Lizard (both 1970), were recorded during a period of instability in the band's line-up, before a settled line-up of Fripp, Sinfield, Mel Collins, Boz Burrell and Ian Wallace recorded Islands in 1971. In mid-1972, Fripp disbanded this line-up, recruited new members Bill Bruford (formerly of Yes), John Wetton, David Cross and Jamie Muir, and changed the group's musical approach, drawing from European free improvisation and developing ever more complex compositions. The band reached what some saw as a creative peak on Larks' Tongues in Aspic (1973), Starless and Bible Black (1974), and Red (1974). King Crimson disbanded at the end of 1974.

After seven years of inactivity, King Crimson was recreated in 1981 with Fripp, Bruford and new members Adrian Belew and Tony Levin. Drawing influence from African music, gamelan, post-punk and New York minimalism, this band lasted three years, resulting in the trio of albums Discipline (1981), Beat (1982) and Three of a Perfect Pair (1984). Following a decade-long hiatus, they reformed in 1994, adding Pat Mastelotto and Trey Gunn for a sextet line-up Fripp called "The Double Trio". The double trio participated in another three-year cycle of activity that included the album Thrak (1995). Fripp, Belew, Mastelotto and Gunn reunited in 2000 as a quartet, called "The Double Duo", releasing The Construkction of Light (2000) and The Power to Believe (2003). After another hiatus, the band reformed for a 2008 tour celebrating the 40th anniversary of their 1968 formation, with Gavin Harrison of Porcupine Tree being added, and Levin returning in place of Gunn.

Following another hiatus (2009–2012), during which Fripp was thought to be retired, King Crimson came together again in 2013, this time as a septet (and, later, octet) with an unusual three-drumkit frontline, and new singer and secondary guitarist Jakko Jakszyk. This version of King Crimson toured from 2014 to 2021. After the band's final show in 2021, Fripp commented that King Crimson had "moved from sound to silence."