The only thing more astonishing than the speed of his combinations was their force, and his ability to blend quickness with brute strength quickly overpowered his early opponents, not many of whom lasted very long in the ring with him. Mr. Berbick, a taller, heavier and more experienced fighter, was done before the second round was over, and what the slow-motion video shows most indelibly is the terror on his face before the referee mercifully called a TKO.

The essence of boxing is violence, but few fighters have refined it — have embodied it — quite as effectively as Mr. Tyson has; he sometimes speaks to Mr. Toback’s camera about the murderous clarity he took into the ring with him. He says he used to imagine his fists smashing through his opponent’s faces and out the backs of their heads. The pure terror in Mr. Berbick’s eyes (and in those of most of the other fighters Mr. Tyson met during his rapid rise and brief reign) suggests that he might well have been capable of wreaking that kind of damage.

But the damage surveyed in “Tyson” is mostly self-inflicted. Fear is certainly one of the film’s motifs, but it seems that Mr. Tyson suffers from at least as much as he inspires. “I’m afraid. I’m afraid. I’m afraid,” he says at one point, giving voice to his state of mind in the moments before a bout. He also remembers being bullied and humiliated as a child in Brooklyn, but in listening to his moody, rambling and frequently thoughtful disquisitions on his own life you are struck by intimations of a dread much deeper than the fear of physical harm or loss of face.

With a single exception — his relationship with his trainer and mentor, Cus D’Amato — Mr. Tyson’s experience of the world has been marked by mistrust and suspicion, by a view of other people that is hard and pitiless. They are users, operators, “leeches,” he says, but he rarely claims to be any better. He is only human.

Most of the movie consists of the former champ sitting in a house near the Pacific Ocean, speaking into the camera as if no one else were around. This produces an effect of almost unnerving intimacy — it is a bit scary to be so close to him — but also an upwelling, perhaps unexpected, of compassion. It is hard to imagine anyone more radically alone.

Whether or not he deserves our sympathy is a fair question. It is easy, and not entirely unjustified, to look at Mr. Tyson, his left eye ringed by a Maori tattoo, his head shaved clean, and see a self-pitying, self-justifying man who squandered his talent and good fortune and caused much more hurt than his brutal profession required. He started out as a street criminal in Brownsville, Brooklyn, and was plucked from juvenile detention by Mr. D’Amato and his associates, who disciplined the young man’s natural volatility and turned him into a fighter.

But Mr. Tyson never learned to control his brutish, self-destructive instincts. His brief first marriage, to the actress and model Robin Givens, was marked by accusations of abuse, and in 1993 he went to prison after being convicted of sexually assaulting a beauty pageant contestant in Indiana. By now he may be better known for ranting and press conferences and for biting Evander Holyfield’s ear during a 1997 fight than for the mighty pugilistic feats of his youth.

And a lot of people, even passionate boxing fans, might prefer to forget about Mr. Tyson rather than spend 90 minutes in his company. But “Tyson” is worth seeing even if you have no particular interest in the sport or the man.

It may lack the detachment and the balance that Barbara Kopple brought to “Fallen Champ: The Untold Story of Mike Tyson,” the 1993 documentary she made for NBC, but Mr. Toback’s film, partly because it restricts itself to Mr. Tyson’s point of view, offers a rare and vivid study in the complexity of a single suffering, raging soul. It is not an entirely trustworthy movie, but it does feel profoundly honest.

From time to time the screen is divided into two or three almost identical images, and the sound is edited to make it sound as if Mr. Tyson is in dialogue with himself, his words echoing and overlapping. These effects emphasize the film’s main point, which is that Mr. Tyson is too mercurial, too self-contradictory, to be easily summed up.

He is by turns boastful, angry, remorseful and bewildered, choking up when he recalls Mr. D’Amato, whose death in 1985 remains the central tragedy of Mr. Tyson’s life. He relates the details of that life with candor and feeling, and also with an analytical ardor that is moving because it reveals his struggle to figure himself out.

Without the sympathetic presence of Mr. Toback, whom he has known for many years, it is unlikely that Mr. Tyson would have opened up in this way. And it is also likely that without Mr. Tyson’s presence, the director would have been unlikely to restrain his own self-indulgent impulses.

Mr. Toback’s fascination with hyperbolic visions of masculinity predates his filmmaking career, going back at least to a notorious 1967 essay on Norman Mailer. As a screenwriter and director — from “Fingers” to “Harvard Man” — he has been preoccupied with brutality, vanity and sexual conquest, and with the interplay between those elemental impulses and the refinements of art and culture.

His protagonists tend to be variously romanticized versions of himself: intellectuals seduced by fantasies of crime, risk, sexual wantonness and violence. Even in his most interesting projects he frequently loses track of the difference between exploring such fantasies and indulging them, but in “Tyson,” his first nonfiction film, he is held in check by the irreducible, excruciating realness of the man in front of the camera. The transaction between them is charged with a strange kind of magic. The filmmaker allows the fighter to have his unchallenged say to justify, condemn and contradict himself. In exchange Mr. Tyson has enabled Mr. Toback to make his best film, which is also, paradoxically, his most personal.

“Tyson” is rated R (Under 17 requires accompanying parent or adult guardian). It has profanity and violence.

TYSON

Opens on Friday in Manhattan.

Directed by James Toback; director of photography, Larry McConkey; edited by Aaron Yanes; music by Salaam Remi, with the song “Legendary” by Nas; produced by Mr. Toback and Damon Bingham; released by Sony Pictures Classics. Running time: 1 hour 30 minutes.