Pink Floyd were an English rock band formed in London. 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 musically influential groups in the history of popular music. Pink Floyd were founded in 1965 by students Syd Barrett, Nick Mason, Roger Waters, and Richard Wright. 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). David Gilmour joined as a fifth member in December 1967; Barrett left the band in April 1968 due to deteriorating mental health. Waters became the band's primary lyricist and, by the mid-1970s, their dominant songwriter, devising the concepts behind their critically and commercially successful 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.