The Rolling Stones are an English rock band formed in London in 1962. As a diverging act to the popular pop rock of the early 1960s, the Rolling Stones pioneered the gritty, heavier-driven sound that came to define hard rock. The band's first stable line-up consisted of bandleader Brian Jones, Mick Jagger, Keith Richards, Bill Wyman, Charlie Watts, and Ian Stewart, the last of whom was removed from the official line-up in 1963, but continued to work with the band as a contracted musician until his death in 1985. The band's primary songwriters, the partnership of Jagger and Richards, assumed leadership after Andrew Loog Oldham became the group's manager. Jones left the band less than a month before his death in 1969, having already been replaced by Mick Taylor, who in turn left in 1974 and was replaced in 1975 by Ronnie Wood, who has since remained. Since Wyman's departure in 1993, Darryl Jones has served as bassist. The Stones have not had an official keyboardist since Stewart's departure in 1963, but have employed several additional musicians in that role, including Jack Nitzsche, Nicky Hopkins, Billy Preston, Ian McLagan, and Chuck Leavell.