April 14, 2008 --Herschel Walker has always been something of a puzzle. As difficult as the star running back was to bring down on the field, it was harder, still, to figure out what made him tick. "I told somebody once, 'You don't want the Herschel that plays football ... babysitting your child," Walker told ABC News correspondent Bob Woodruff. "When I am competing, I am a totally different person.'" He means it literally. For the first time, the 46-year-old former professional football player reveals in a book published this week, "Breaking Free," that he has a rare and controversial mental illness called dissociative identity disorder ? or D.I.D. ? formerly known as multiple personality disorder. "I had it the whole time, I just didn't know what it was," Walker said. The athlete who played 15 seasons of professional football in the NFL and USFL and pushed a bobsled for the 1992 U.S. Olympic team in Albertville, France; the family man who married his college sweetheart; the man who once danced with the Fort Worth Ballet; the business man ? Walker says none of those guys were him. Not really. Those were his "alters," he says -- alternate personalities. Walker's family, former teammates and fans reacted to the revelation with shock. "I know him better than anybody 'cause I raised him," Walker's father, Willis Walker Sr. told the Atlanta Journal-Constitution in January. "This is my first knowing about that." The disorder usually has its roots in childhood trauma. "I was a fat little kid with a speech impediment," Walker told Woodruff. "I used to get beat up, not just picked on." Walker's therapist Jerry Mungadze, said he met Walker's alternate personalities, or alters, in therapy. "They will come out and say, I am so-and-so. I'm here to tell you Herschel is not doing too good ... When he finishes, it would just disappear back in him, and Herschel comes out." Walker and Mungadze believe the disorder actually helped Walker ? who started for a number of NFL teams, including the Minnesota Vikings and the Dallas Cowboys ? succeed on the gridiron. Mungadze offered a theory about the subconscious logic in Walker's head. "Since people are laughing at you, we're going to make you so strong, so fast, so talented, that you're going to be above everyone. And that is what went into building this super athlete." Married to Many But shortly after retiring from football, Walker descended into mental mayhem. At one point, Walker says he sat alone at his kitchen table and played Russian roulette with a loaded pistol. Walker told Woodruff, "To challenge death like I was doing, you start saying, there's a problem here." Walker's diagnosis answered a lot of questions for Walker's ex-wife Cindy Grossman, who was married to Walker for 16 years before she knew about the illness. "Well, now it makes perfect sense, because each personality has a different interest. This one has an interest in ballet, this one has an interest in the Marines, this one had an interest [in the] FBI, this one had an interest in sports," she said. Grossman recognized different sides of her husband, even different voices. "It's hard to explain, but even his physical countenance would change. ... There was also a very sweet, lovable [personality]. That's the one he told me I married. He told me I didn't marry Herschel." But there were darker moments. "We were talking and the next thing I knew," Grossman remembered, "he just kind of raged and he got a gun and put it to my temple.'" Walker's ex-wife now believes one of his alternate personalities was in control at that moment. "There was somebody there that was evil." 'If I Can Remember It, I'll Talk About It' Walker says he does not remember the event, and many others, including ? shockingly ? the highlight of his collegiate football career, winning the Heisman Trophy in 1982. Periods of memory loss are one of the symptoms of the disorder. "A lot of the things that happened there that she may remember, he doesn't remember because those were the things that were being done by the alters that were so unlike him," Mungadze explained. "Do you not remember something like that because you think that was another alter," Woodruff asked, "or do you want to get out of having to talk about it?" "No, no, no, no," Walker insisted. "I'm talking about everything else. If I can remember it, I'll talk about it." There were other incidents Walker does not recall. "I was pregnant and it was probably 100 degrees out," Grossman said. "Herschel was dressed in a full sweat suit, tights, sweats, jacket, and he was running through the house. ... he said, 'Close the door. I am having bad thoughts. I am thinking I am going to hurt you.'" On another occasion, Walker threatened to kill his wife, his wife's friend and his therapist in a therapy session. Mungadze said he saw many alters on that day: a raging one, a protector, and finally a child when Walker hit a wall and broke his hand. Walker does not deny the events, but says he has no memory of them. "No, I don't remember that, but I probably did it." After a hospital trip to treat Walker's hand, Grossman remembers Walker calling her, "'Miss lady." "And I said, 'My name is Cindy.' And he said, 'Herschel's hungry. Do you know what he likes to eat?'" she recalled. "I said, 'Well, I know he likes wings." "People outside ? Cindy, Pastor Evans, Doctor Jerry ? may have seen that, whereas I may not remember a lot of that," Walker told Woodruff. "And I hear them say that, and I say, 'Oh, that's weird.'" Living as 'We' Instead of 'I' It is difficult to understand how someone with this disorder sees the world. "It's just personalities that can do different things for you," Walker said. Mandgadze offers a metaphor. "It's like a teacher in a classroom, a very chaotic classroom, where the students do what they want to do ? hit each other, scream ... we would like them to have some way of managing his alters, almost like a teacher manages students." "But we all do that. We get angry or we get frustrated; our eyes change, our face changes, right?" Woodruff asked Mungadze. "No, not to that extent," Mungadze replied. "There are a lot of doctors that say, 'We don't think this exists, this D.I.D.," Woodruff asked Grossman. "That makes me kind of angry," replied Grossman. "I just know he has it. I know what I saw." The Diagnostic and Statistical Manual of Mental Disorders defines the disorder as "the presence of two or more distinct identities or personality states that recurrently take control of behavior." The alternate identities "frequently have different names and characteristics that contrast with the primary identity." In the book, Walker names around a dozen alters, including "The Warrior" who handled football and the pain that came with it. "The Hero" took over in public appearances. Woodruff asked which alters are good and which are bad. "Oh, there's a lot of bad ones in there," Walker answered. Sometimes, Walker says, the alters disagree about the diagnosis. "Sometimes I tell myself, 'Herschel, that's bunch of crap. That's not real.' There's moments, but then I say that maybe it's just an alter trying to fool me. They say, 'Herschel, that ain't right.'" Walker has been in treatment for eight years but takes no medication. He feels he has brought the unruly classroom in his head more under control. "I've totally changed from back then to where I am today." Mungadze described the steps of therapy as acceptance of the alters and then assimilation of their functions into the main individual. Writing the book was therapeutic for Walker. He hopes its publication will change the public's image of the disorder and help other people with the disorder. "D.I.D. is not 'Sybil' or 'Three Faces of Eve.' D.I.D. is just an illness that people are dealing with," Walker said. In "Breaking Free," Walker wrote, "I feel the greatest achievement of my life will be to tell the world my truth."