'For No Good Reason' (R)

It sounds mundane, the way Ralph Steadman describes what he does. The essence of his work, he says, is “to distort, and yet maintain the likeness.”

The English artist, illustrator, and cartoonist, famous for his 1970s Fear and Loathing adventures with notoriously fried journalist Hunter S. Thompson, comes off as surprisingly mild-mannered and, well, sane in For No Good Reason, an illuminating and suitably hyperactive documentary portrait.

Steadman, a fit-looking septuagenarian who lives in a splendid house in the English countryside, points to painter Francis Bacon as an idol and an influence. Steadman’s style — bold splats of ink, maniacal, elongated figures, blotched in colors of blood and crud — captures the troubled, restless regions of his subjects’ psyches, be they rock stars, royalty or skid row derelicts.

Directed by Charlie Paul, a British video and commercial maker who grew up during punk music’s first wave and recognized a kindred spirit in Steadman, For No Good Reason was filmed, off and on, over 15 years. He stationed a camera over Steadman’s drawing table — a dangling-spider’s-eye view of the artist at work.

Johnny Depp, who portrayed Thompson’s drug-and-drink-addled alter ego in the 1998 film Fear and Loathing in Las Vegas, is invited for a visit. The movie star with the battered hat and designer glasses stands over Steadman’s work table, scanning drawings, riffling admiringly through one of the published collections of his earlier work. Then Depp and Steadman go misty, recalling Thompson, the gonzo scribe they both knew, who blew his brains out in 2005.

There is telling footage of a younger Steadman and Thompson mulling what their relationship meant, and how their respective words, and drawings, mattered. Terry Gilliam, who directed Depp in Fear and Loathing, chimes in with his take on the Thompson/Steadman collaboration. And there is scary-beautiful film of a creaky, old, gunslinging William S. Burroughs taking potshots (with revolver and shotgun) at a portrait of Shakespeare. That was Steadman’s idea, a kind of performance art, truly creepy.

Paul is keen on collage-ing up his visuals, animating a few of Steadman’s drawings (very cool), creating stagy tableaus, mixing video and vintage celluloid, layering on thickets of music. Still, the documentary remains remarkably calm amid all the busyness. Observant, respectful.

And though we don’t get to know Steadman the man all that well (rough time at boarding school, and yes, he has a wife and a dog), we do get to know his art.

That alone is worth the trip.

With: Ralph Steadman, Johnny Depp, Hunter S. Thompson, Terry Gilliam, Richard E. Grant, Jann Wenner.

Director: Charlie Paul.

A Sony Pictures Classics release. Running time: 89 minutes. Vulgar language, drug content, brief nudity. Opens Friday June 6 in Miami-Dade: South Beach; in Palm Beach: Shadowood