Slash, Jason Mraz, Richard E. Grant and Terry Gilliam have added music and memories to Johnny Depp's new movie about artist Ralph Steadman.

Depp signed on to narrate documentary For No Good Reason about the life and work of the British cartoonist last year (13), and the finished film also features many other famous friends.

Created over 15 years by filmmaker Charlie Paul, For No Good Reason includes footage of Steadman at work and anecdotes from late writer Hunter S. Thompson, who formed a bond with the Brit in the 1970s and used his illustrations in books like Fear & Loathing in Las Vegas, which was adapted for the big screen and starred Depp.

Gilliam, who directed the 1998 film, and Grant offer tributes, while Steadman fans Slash, All American Rejects, Mraz, James Blake, Ed Harcourt and Crystal Castles created music for the film's soundtrack.

For No Good Reason opens in limited release in America later this month (Mar14).