Keith John Moon (23 August 1946 – 7 September 1978) was an English drummer for the rock band the Who. He was noted for his unique style and his eccentric, often self-destructive behaviour.

Moon grew up in Alperton, a suburb of Wembley, in Middlesex, and took up the drums during the early 1960s. After playing with a local band, the Beachcombers, he joined the Who in 1964 before they recorded their first single. He remained with the band during their rise to fame, and was quickly recognised for his drumming style, which emphasised tom-toms, cymbal crashes, and drum fills. Throughout Moon's tenure with the Who his drum kit steadily grew in size, and (along with Ginger Baker) he has been credited as one of the earliest rock drummers to regularly employ double bass drums in his setup. Moon occasionally collaborated with other musicians and later appeared in films, but considered playing in the Who his primary occupation, and remained a member of the band until his death. In addition to his talent as a drummer, however, Moon developed a reputation for smashing his kit on stage and destroying hotel rooms on tour. He was fascinated by blowing up toilets with cherry bombs or dynamite, and by destroying television sets. Moon enjoyed touring and socialising, and became bored and restless when the Who were inactive. His 21st birthday party in Flint, Michigan, has been cited as a notorious example of decadent behaviour by rock groups.

Moon suffered a number of setbacks during the 1970s, most notably the accidental death of chauffeur Neil Boland and the breakdown of his marriage. He became addicted to alcohol, particularly brandy and champagne, and acquired a reputation for decadence and dark humour; his nickname was "Moon the Loon". After moving to Los Angeles with personal assistant Peter "Dougal" Butler during the mid-1970s, Moon recorded his only solo album, the poorly received Two Sides of the Moon. While touring with the Who, on several occasions he passed out on stage and was hospitalised. By the time of their final tour with him in 1976, and particularly during production of The Kids Are Alright and Who Are You, the drummer's deterioration was evident. Moon moved back to London in 1978, dying in September of that year from an overdose of Heminevrin, a drug intended to treat or prevent symptoms of alcohol withdrawal.

Moon's drumming continues to be praised by critics and musicians. He was posthumously inducted into the Modern Drummer Hall of Fame in 1982, becoming only the second rock drummer to be chosen, and in 2011, Moon was voted the second-greatest drummer in history by a Rolling Stone readers' poll.