NEW YORK — Heisman Trophy winner Herschel Walker once played Russian roulette with a loaded pistol as he struggled with a personality disorder.

"To challenge death like I was doing, you start saying, there's a problem here," he said during an interview to be broadcast tonight on ABC's "Nightline."

Walker suffers from dissociative identity disorder, formerly known as multiple personality disorder. His experiences are chronicled in his book, "Breaking Free," which is released this week.

The 46-year-old Walker was a star running back at Georgia and in the pros. He says he had the condition during his playing days but didn't realize it. He doesn't remember winning the Heisman in 1982 or darker events, such as threatening his then-wife.

Walker has been in treatment for eight years but doesn't take medication. He believes he has improved greatly.

"I've totally changed from back then to where I am today," he says.