WRIGHTSVILLE, Georgia (CNN) -- Many people think they know the legendary Herschel Walker: 1982 Heisman Trophy winner, pro football star, Olympian and last week in San Francisco, an Olympic torchbearer.

Herschel Walker says he wrote about his dissociative identity disorder to dispel myths and help others.

But not only did the public not know the real Herschel Walker, the athlete himself said he didn't either. In his just-released book "Breaking Free," Walker reveals he has a form of mental illness called dissociative identity disorder, or DID, formerly known as multiple personality disorder.

"I didn't really learn about this until about 10 years ago," Walker tells CNN. "My life was out of control. I was not happy, I was very sad, I was angry and I didn't understand why."

Walker said his life went off the tracks shortly after his football career ended and when his now ex-wife was expecting their son, Christian.

The book, he said, is about coming to terms with his diagnosis. He hopes to educate the public and break down stereotypes about this disorder.

When people hear of multiple personality disorder, they may think of Hollywood's portrayal -- someone with different "people" trapped inside one body, but that is not accurate.

Everyone has various facets that make up his or her personality -- assertive, angry, comforting. But, experts explain, in DID, these various parts -- known as alters -- don't come together as one cohesive single personality. Instead, one or the other part of the identity takes over and determines one's behavior. Watch Herschel Walker talk about his personality disorder with Dr. Sanjay Gupta »

Asked how many different personality facets, or alters, he has, Walker replied: "To be honest, I have no idea." But in the book, Walker talks about a dozen. They're described by their roles or function: the Hero, the Coach, the Enforcer, the Consoler, the Daredevil, the Warrior, to name a few.

Some of these alters did a lot of good, he said. But others led to some extreme and violent behavior, most of which Walker said he doesn't remember. As a result, the disorder, or DID, led to the breakup of his marriage. "I lost the person that was like everything to me," he said. "I lost my wife and that's totally, totally devastating to me."

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Walker said a competitive alter caused him to be a danger to himself, playing Russian roulette more than once. In the book he describes another incident, the very late delivery of a car, that made him so angry he had thoughts of killing someone. It was the moment he realized had to seek help, he said, which ultimately led to his diagnosis.

Nobody witnessed his alters surfacing more than Cindy Grossman, now remarried, but who was Mrs. Herschel Walker for 19 years.

For 16 years of her marriage, Grossman said, she didn't know anything was wrong. That's because Walker's various alters were somehow kept in check. He believes during that time, his alters did a lot of good. They helped him train hard to become an outstanding athlete and student, smashing high school football records, graduating at the top of his class and evolving into one of the greatest college football players ever.

When football was out of Walker's life, his alters were no longer focusing on a common goal. That's when things started to go wrong. Dr. Jerry Mungadze, Walker's therapist, said he's seen at least three of Walker's alters and believes that after retiring from football, Walker "had to find another way of coping and couldn't." That search led to the chaos in Walker's life. Blog: Dr. Sanjay Gupta on Walker's disorder

Grossman said that after Walker learned he had DID, things got a lot worse. She remembers the emotional extremes: "Very violent alters and very sweet alters." When the bad alters surfaced, she said, Walker sounded different and his eyes would get "evil -- I remember just getting chill bumps when he looked at me."

She said that Walker held a gun to her head a handful of times. He also threatened her with knives. She remembers one situation where at least two alters were involved: She was in bed and couldn't see very well because she didn't have her contact lenses in. Suddenly, she said, Walker threatened her with a straight razor. "He had it to my throat and kept saying he was going to kill me... think he choked me. I think I passed out.

"When I came to, there was someone else there [saying] 'Cindy, Cindy, Cindy. Wake up, wake up!' "

Walker said he doesn't remember the assault, but he also doesn't deny it. "One of the symptoms of DID is blackouts," he said. "I do not remember certain events. Cindy and Dr. Jerry Mungadze have relayed confrontations which have been violent or aggressive, but I have no memory of any of it. I'm troubled by my actions and will always deeply regret any pain I've caused Cindy. Cindy has been a tremendous help in aiding my therapy and the integration of my personalities. That's why I wrote the book -- to assist others." Read an excerpt

There are no precise numbers on how many people suffer from DID. But Stanford University psychiatrist Dr. David Spiegel has been studying multiple personalities for more than 30 years. He estimates DID affects about 1 percent of the U.S. population.

He is not one of Walker's doctors, but he said what Walker described is consistent with DID.

Health Library MayoClinic.com: Dissociative disorders

Spiegel said DID is really a childhood disorder, which usually isn't diagnosed until adulthood. DID stems from trauma, physical and psychological abuse suffered as a child, when the brain is still developing a personality. "It's a natural response to overwhelming repeated trauma."

Walker said his trauma occurred in elementary school. He writes " I was fat... with a severe stuttering problem." Standing outside the now rundown building that used to be his elementary school, he said he had very few memories of his time there, except, "I remember this guy beating me up."

"I used to get beat up a lot, and I couldn't fight back."

Spiegel said physical abuse doesn't have to be by a family member and so being teased relentlessly and getting beaten up meets the criteria for DID, as is not remembering key events in one's life.

There are no drugs to treat DID. "It's hard to get treatment and there's no quick fix, but psychotherapy helps," and people can get better, according to Spiegel.

Walker's alters did not appear in his interview with CNN. He seemed very friendly and generous. Mungadze attributes that to the therapy Walker has undergone so far.

Walker is aware that his revelation may lead to ridicule or doubt. "I'm fine with that," he said. "I'm ok. I love me -- Herschel Walker. You know 10 years ago I probably couldn't say that. But today, I can say that. I'm not going to say I'm great or I'm good, but I'm OK. E-mail to a friend

Miriam Falco is a managing editor of CNN Medical News.