In the inevitable argument over who would win in a hypothetical fight between Muhammad Ali and Mike Tyson, I stump for Tyson. This has less to do with technical analysis than a lizard brain recognition of a fighter whose physical strength is fueled by a deeply ingrained, skinless ferocity—he is simply the most frightening human being I can contemplate having to face in hand-to-hand combat.

It makes an odd sense that in James Toback's disarming new documentary, Tyson, his subject's full range of emotion reverberates as close to the surface as his murderousness did in the ring. Here Tyson expresses pain with as much honesty as he inflicted it, with a surprisingly unguarded level of candor and eloquence. It seems strange the first time Tyson cries on camera, and when he does it again afterward, you never quite get used to it.

Tyson is something beyond a simple biographical documentary. Intensely confessional and self-reflective, the idea of the film languished for years, until the stars aligned for both fighter and filmmaker to latch onto it as an emotional lifeboat: Tyson had just crashed his car and landed in rehab for cocaine addiction, while Toback had just lost his mother, and had, as he delicately puts it, "found myself doing things that I felt would abbreviate my life." So they holed up in a rented Hollywood Hills house and made something constructive out of their anguish.

It's unlikely that a documentary about Mike Tyson this revealing could have been made by another filmmaker, and according to Toback, Tyson actually turned down a lucrative offer from Werner Herzog. With a friendship spanning more than 20 years, Toback explains that Tyson "knew that I wouldn't ridicule him."

Indeed, who would dare? In Tyson, the fighter describes his life's beginning as an asthmatic, short, fat kid who was often the subject of ridicule. The anxieties of his childhood, coupled with a pubescent career in drugs and the juvenile detention system, primed him through physical and psychological injury to channel his fears, through boxing's edifying rigors, into fight. It's a superhero's story as much as it is a Greek tragedy, which is how Tyson himself described it to Toback after first seeing it—telling him, "I was watching, and thinking how people think I'm crazy and they're scared of me. Watching it, I thought, 'I'm scared of this guy.'"

Indeed, Tyson hardly glosses over the most threatening chapters of his life. It's easy to empathize with his side of the story when he recalls biting Evander Holyfield's ears mid-fight after multiple illegal head butts. Likewise, the betrayal he felt by Robin Givens during an over-scrutinized, doomed marriage marked by allegations of domestic abuse. But his denial of having committed rape, despite having been convicted, is a disquieting thing to swallow alongside intimate self-descriptions of the animal violence of his sexual appetite.

Such disclosures are delivered in a dizzying almost-prose, relayed in film through a split-screen technique that brings you right into Tyson's eyes and his mouth. It's an effective device, one that Toback had toyed with in the past, but was ultimately compelled by the potential it held to illustrate an icon as complex and fragmented as Mike Tyson. It was, as he says, much like the union of Tyson with boxing, of fear with violence, "an urgent connection."