Illustration by Ralph Steadman, Courtesy of Sony Pictures Classics. (Ralph Steadman, Courtesy of Sony Pictures Classics)

“Rolf! ROLF!”

Ralph Steadman, that great gonzo artist, is barking over the phone like a beast, a baritone woof that summons thoughts of those ferocious hellhounds he paints to grace the beer bottles that clank out of the Flying Dog brewery in Frederick.

“Rolf! ROLF!” Steadman says in clipped diction, mimicking how his old journalistic running mate, the late, celebrated Hunter S. Thompson, used to pronounce the artist’s first name. Steadman is recounting the mantra for their every shared wild-eyed assignment — whether they were famously chronicling ’70s Kentucky Derby debauchery, or Rolling Stone’s “Fear and Loathing” on some hot fresh campaign trail. Each time the artist would ask why, and each time the rabid Thompson would reply:

“Rolf! We’re doing this for no good reason.”

Steadman is sharing stories to promote his new bio-documentary, “For No Good Reason,” filmed at his bucolic “castle” of a stone-walled Georgian estate in Kent, England, where he greets narrator and friend Johnny Depp at the gate.

Steadman’s greatest American fame came because of his artistic impressions of — and with — Hunter S. Thompson. (Courtesy of Ralph Steadman/Sony Pictures Classics)

The actor, of course, has thrice played Thompson on screen; he inhabits a jabber-mouthed madman, a loon of a cartoon. On cue, Steadman can summon the same voice, that galloping patter. So which impersonator does a better Thompson?

“I do a better one than Johnny Depp,” assures Steadman.

It’s only natural that Steadman does a better impression of Thompson, since his greatest American fame came because of his artistic impressions of — and with — Thompson. They were the raw, intoxicating gonzo teammates who changed one face of journalism — even if that face featured a dangling cigarette holder, big tinted glasses and a floppy hat like comic props. Steadman’s sublime paint-slung portraits of Thompson helped cement the writer on the Rushmore of countercultural reporting. Thompson, dead since 2005, still gets his due. But let us not forget the simpatico artist who fixed that image in our skulls.

In the new film, we see Steadman surrounded by turrets of Winsor Newton brushes and tubes of gesso paint, comfortable in the spotlight, at the table where for decades the spontaneous magic has happened. He comes across as a kind-eyed, bespectacled grandpa who happens to render dramatic images to trouble the soul.

The husband-and-wife filmmaking team of Charlie and Lucy Paul took years to get here — the artist in his natural habitat. Charlie, the London director, first approached Steadman in the late 1990s, via letter. The artist’s reply from Kent: “Come see rather than try to imagine. Come down. That’s the only thing of value.”

The director and his subject spent years developing a warm rapport — even as the filmmaker put a digital camera over Steadman’s table, so the artist could photograph his works in progress whenever he liked. “That was marvelous — one of the few useful things to come out of technology, the memory card,” Steadman says.

Both physically and emotionally, Steadman’s art is all about impact — paintbrush as flung weapon, like a lunge at our psychic gut. “It’s a direct response,” Charlie Paul says while seated in a hotel conference room in Georgetown. “His art is the moment a fly hits the windshield.”

That image gets at Steadman’s spontaneous, action-splattered aesthetic. Yet everything within that painted violence is precise. “He hates drips,” Paul says. “Ralph has complete control — he’s a master of his ink.”

Given the organic stagecraft to Steadman’s creation, the filmmakers learned to anticipate when and where to move their cameras. “If you’re not there, you miss it,” says producer Lucy Paul. “It’s like a ballet.”

The film is an intentionally non-linear journey through Steadman’s life and career — from animations of his still art to closeups with such knowing colleagues as Monty Python’s Terry Gilliam and Rolling Stone honcho Jann Wenner. And we get, naturally, vintage video of Thompson; Steadman and Charlie Paul agreed not to shoot fresh footage of Hunter while he was alive, lest he overtake the film in his outsize manner.

Thompson is nearly omnipresent, though, as twin narratives often power this film. The first is the posited twist that though Thompson had the rep as the wild man, the seemingly more mild-mannered Steadman burned with a deeper capacity for the crazy. (Although Thompson was known for his prodigious drinking, Steadman notes, “I never saw him drunk.”) The second related narrative centers on the question: How can such a nice man make such violently disturbing images?

Both narrative roads lead to the same home truth: Steadman. Hates. Bullies.

He is a onetime Wales choirboy who was caned by an abusive school headmaster. Out of that, the director says, Steadman developed the need to speak out against “something that is just wrong — whether it’s starvation or dictators.”

“Bullies? Yeah, like [Saddam] Hussein, or Nixon, I think it’s lovely to shove [such] people around on paper,” says Steadman, who also became famous for his politically charged Watergate-era work. “I think Nixon was a son of a b----.”

Even in his non-“political” illustrations, Steadman makes a statement. “I wonder sometimes when people just become artists, why they just paint what they [see],” with no opinion or sentiment. “You’ve got to make a comment.”

In the film, Steadman likes to use masking fluid, which by erasure helps reveal elements within his work. Likewise, in his visual commentary, Steadman is motivated to strip away the aura of official authority, which he deeply distrusts as a mask for violence.

That speaks to why Steadman, as a young man, felt so compelled to make political art: He wanted to change the world. Looking back now, at 77, he’s not so sure he did.

His advice to the next generation is “maybe not to become cartoonists, but to become doctors, and nurses, too. Become social reformers. Turn out a whole generation of reformers.

“Don’t follow the path of scribbling ink on paper,” he says of the tools of change. “Get yourselves a big hammer!”

The filmmakers see far more potential influence in Steadman’s illustrated legacy. “We made this film for my kids’ generation,” Charlie Paul says. “If they pick up even 10 percent of Ralph’s outlook on life, it’s worth it.”

Meaning, of course, his life of scribbling ink on paper has been for a good reason after all.

For No Good Reason

Rated R. At Landmark’s E Street Cinema. Contains crude language, drug content and sexual imagery. 89 minutes.