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, English-accented singing, and stream-of-consciousness writing style. 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 fewer than ten years. With Pink Floyd, he recorded the first four singles, their debut album The Piper at the Gates of Dawn (1967), portions of their second album A Saucerful of Secrets (1968), and several songs that were not released until years later. In April 1968, Barrett was ousted from the band amid speculation of mental illness and his use of psychedelic drugs. He began a brief solo career in 1969 with the single "Octopus", followed by albums The Madcap Laughs (1970) and Barrett (1970), recorded with the aid of members of Pink Floyd.

In 1972, 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 to him, 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.