Roger Keith "Syd" Barrett (6 January 1946 – 7 July 2006) was an English singer, guitarist and songwriter who co-founded the rock band Pink Floyd in 1965. Until his departure in 1968, he was Pink Floyd's frontman and primary songwriter, known for his whimsical style of psychedelia and stream-of-consciousness writing. As a guitarist, he was influential for his free-form playing and for employing effects such as dissonance, distortion, echo and feedback.

Trained as a painter, Barrett was musically active for just over ten years. With Pink Floyd, he recorded the first three singles, their debut album The Piper at the Gates of Dawn (1967), part of their second album A Saucerful of Secrets (1968), and several songs that were not released until later. He left the band in April 1968 amid speculation of mental illness and his use of psychedelic drugs, beginning a brief solo career the following year with the single "Octopus", followed by albums The Madcap Laughs (1970) and Barrett (1970), recorded with the help of Pink Floyd and the Soft Machine.

In 1974, Barrett left the music industry, retired from public life and guarded his privacy until his death. He continued painting and dedicated himself to gardening. Pink Floyd recorded several tributes and homages, including the 1975 song suite "Shine On You Crazy Diamond" and parts of the 1979 rock opera The Wall. In 1988, EMI released an album of unreleased tracks and outtakes, Opel, with Barrett's approval. In 1996, Barrett was inducted into the Rock and Roll Hall of Fame as a member of Pink Floyd. He died of pancreatic cancer in 2006.

Roger Keith Barrett was born on 6 January 1946 in Cambridge as the fourth of five children to a middle-class family living at 60 Glisson Road. His father, Arthur Max Barrett, was a prominent pathologist and was said to be related to Elizabeth Garrett Anderson through Max's maternal grandmother Ellen Garrett. In 1951, his family moved to 183 Hills Road, Cambridge.

Barrett played piano occasionally but usually preferred writing and drawing. He bought a ukulele aged 10, a banjo at 11 and a Höfner acoustic guitar at 14. Initially playing acoustic guitar, he later purchased a Selmer Futurama III, electric. He was a Scout with the 7th Cambridge troop and went on to be a patrol leader.

Barrett reportedly used the nickname Syd from the age of 14, derived from the name of an old Cambridge jazz bassist, Sid "the Beat" Barrett; Barrett changed the spelling to differentiate himself. By another account, when Barrett was 13, his schoolmates nicknamed him Syd after he came to a field day at Abington Scout site wearing a flat cap instead of his scout beret, because "Syd" was a "working-class" name. He used both names interchangeably for several years. His sister Rosemary said: "He was never Syd at home. He would never have allowed it."

At one point at Morley Memorial Junior School, Barrett was taught by the mother of his future Pink Floyd bandmate Roger Waters. Later, in 1957, he attended Cambridgeshire High School for Boys with Waters. His father died of cancer on 11 December 1961, less than a month before Barrett's 16th birthday. On this date, Barrett left the entry in his diary blank. By this time, his siblings had left home and his mother rented out rooms to lodgers.

Eager to help her son recover from his grief, Barrett's mother encouraged the band in which he played, Geoff Mott and the Mottoes, a band which Barrett formed, to perform in their front room. Waters and Barrett were childhood friends, and Waters often visited such gigs. At one point, Waters organised a gig, a CND benefit at Friends Meeting House on 11 March 1962, but shortly afterwards Geoff Mott joined the Boston Crabs, and the Mottoes broke up.