There's a sketch of two lumpy, misshapen heads side by side on a sidewalk, each with a panhandler's tin cup in front of him. The one with two eyeballs, looking at the other with one and an eye patch says, "People like you are a real inspiration to me!" It's signed CALLAHAN.

John Callahan was an irreverent Portland wiseguy who thought that his having been ruinously injured in a car crash was a sick joke. He permanently lost the use of his legs, and when he regained partial use of his arms, he began turning out offbeat, deadpan cartoons about disabled people.

His drawings were eruptions of pitch-black humor that seemed politically incorrect even for the hippie-dippy 1970s and '80s. They were also popular. His work was syndicated by 200 newspapers worldwide. Still, he didn't leave a lasting influence like Robert Crumb, or even a passing marketing phenomenon like R. Kliban's coffee table books of cat cartoons. When he died in 2010 at 59, he was gone and largely forgotten.

Out of that obscurity, Callahan has become the subject of a dramatic biography, "Don't Worry, He Won't Get Far on Foot," in which he's played by Joaquin Phoenix, who learned about the quadriplegic alcoholic for the first time when director Gus Van Sant asked him to take the part. The film, loosely adapted from Callahan's life, is as divisive as his work, sure to be considered brutally funny by some and brutally insensitive by others.

It takes its title from a cartoon that illustrated Callahan's 1989 autobiography. In a desert sandscape, a sheriff's posse on horseback studies an empty wheelchair. The leader tells his deputies, "Don't worry, he won't get far on foot."

Phoenix, a true chameleon, captures that tone of self-directed wit and an ocean of anger. He shows us a sworn nonconformist from every angle. We see the immature, alcoholic rebel against authority that Callahan was before the accident. And after the crash, we see the stunned survivor facing endless rehabilitation, the sly, flirtatious, rather dashing romantic on wheels and the determined artist holding a pen in his right hand as his left steers it across a sheet of paper, creating insidious, idiosyncratic jokes.

The film trampolines across Callahan's life out of chronological order, like flipping at random through an old diary, moments of drama here, doldrums there. Through it all, Phoenix gives us a sense that we're seeing a life being lived, not impersonated. In a charged sequence where he drops a wine bottle and nearly kills himself trying to retrieve it, or a knockabout turn when he races some kids with his motorized wheels, bursting out laughing after he inevitably crashes, there's a near-documentary sense of acutely captured reality. It's the kind of work that rightly draws attention at awards season.

Nevertheless, watching the film, which Van Sant also wrote, can be exhausting. Much of it is focused on Callahan's long fight against his alcohol addiction, with guidance from his AA sponsor Donny (an understated Jonah Hill). His repeated steps on and off the wagon become tedious.

One wishes the film gave more focus to its supporting characters. They deserve it. Jack Black has a stunningly strong turn as the drunken driver who rocketed the equally unconscious Callahan into a telephone pole at 90 miles an hour, emerged unscathed, and carried that guilt for the rest of his life. As Callahan's unlikely late-in-life girlfriend, a Swedish airline stewardess named Annu, Rooney Mara brings a benign energy without being a trite Cinderella. If the film were less a drama about recovery and more a group portrait of such intriguing, underused characters, it would be a real inspiration.