A new documentary by filmmaker James Toback shows how a small, scared kid with breathing problems became one of the most fearsome and infamous boxers of all time -- and one of the most controversial and tormented figures in sports.

In an appearance on Canada AM on Thursday, Toback spoke about his award-winning documentary that features Tyson speaking candidly about his early years and how his experiences led to his polarizing reputation: simultaneously he was one of the most dominating fighters in boxing history but he also spent three years in prison after being convicted of rape.

"He's incapable of censoring himself, so you're getting this kind of unadulterated truth all the time," said Toback.

Toback described young Tyson as a "short fat kid" with breathing problems possibly caused by undiagnosed asthma. He compared it to his own childhood asthma, which gave him a constant feeling of panic.

"Either you can't breathe or you're afraid you're not going to be able to breathe," explained Toback.

Toback explained these problems had a lasting impact on Tyson, who spoke constantly "about how afraid he was all the time, his pervasive sense of fear," in the documentary.

But boxing gave Tyson the chance to tap into and use those feelings to his benefit.

"He took the panic and the fear and went to the other extreme, into total rage and total brutality," explained Toback.

"It's as if to say I'm not going to be a weakling, I'm not going to be suppressed. I'm going to destroy you."

While at first glance "Tyson" sounds like a film that would appeal solely to boxing fans, Toback claimed it has a wider appeal and said even women who don't like boxing or Tyson are enjoying it.

"They're the ones who in many cases have tears in their eyes, who say I want to give him a hug," he explained. "They're the ones who are absolutely taken by it."

He thinks this emotional impact comes from how candidly Tyson speaks about his life.

"He is defiantly and willfully unconcerned about what people think. He literally prides himself on saying 'let them think what they want, I don't care'," he added.

It's this straight talk by Tyson that Toback feels draws the audience to his movie.

"Any time he starts talking, everybody's listening, everybody's looking at him... he's a hypnotic figure."

Toback said that even during editing, he could tell "Tyson" was going to resonate with viewers.

He tested his idea by enticing women to watch his movie with a unique offer: "If you want to leave after five minutes, I'll give you a $100 for having come. If you stay until the end, you don't get anything."

Toback claimed that all of the 35 women he invited stayed for the whole movie.

At the height of his career, Tyson had a record of 39 wins and no losses. But after his 1989 divorce from Robin Givens, his career began to decline. The next year he lost the heavyweight championship to Buster Douglas and in the summer of 1991 Tyson was arrested and charged with rape. He was convicted and served three years in prison.

After his release he returned to boxing, a comeback best remembered for an infamous fight in 1997 against Evander Holyfield where Tyson bit off his opponent's ear.

Tyson retired from boxing in 2004.

Toback's documentary is the fruit of a 25-year relationship between him and Tyson. He met Tyson in 1985, during the production of "The Pick-up Artist" and the two struck up a relationship that led to Tyson starring in two of Toback's movies: "Black and White" and "When Will I Be Loved".

After finishing "Black and White" in 1999, Toback approached Tyson about doing a documentary on him.

He said that Tyson was immediately receptive to the idea. "He said if you want to do it, let's do it."

At its debut at last year's Cannes Film Festival, "Tyson" won the Knockout award in the Un Certain Regard sidebar competition.

The documentary opens in Montreal, Toronto and Vancouver on Friday, May 8.