Pink Floyd were an English rock band formed in London in 1965. They achieved international acclaim with their progressive and psychedelic music. Distinguished by their use of philosophical lyrics, sonic experimentation, extended compositions, and elaborate live shows, they are one of the most commercially successful and influential groups in popular music history. Pink Floyd were founded by students Syd Barrett on guitar and lead vocals, Nick Mason on drums, Roger Waters on bass and vocals, and Richard Wright on keyboards and vocals. They gained popularity performing in London's underground music scene during the late 1960s, and under Barrett's leadership released two charting singles and a successful debut album, The Piper at the Gates of Dawn (1967). Guitarist and vocalist David Gilmour joined in December 1967; Barrett left in April 1968 due to deteriorating mental health. Waters became the band's primary lyricist and conceptual leader, devising the concepts behind their albums The Dark Side of the Moon (1973), Wish You Were Here (1975), Animals (1977), The Wall (1979) and The Final Cut (1983). The Dark Side of the Moon and The Wall became two of the best-selling albums of all time.