They called him Sweetness, but Bears great Walter Payton had a dark side, according to a biography to be released Oct. 4. An excerpt of "Sweetness: The Enigmatic Life of Walter Payton," by Jeff Pearlman, will appear in the Oct. 3 issue of SI, and describes the Hall of Famer as suicidal, abusing pain medication and dealing with a crumbling family situation. Payton, who retired after the 1987 season as the then-all-time leading rusher in NFL history, was depressed and suicidal in the mid-1990s. Pearlman cites a letter from Payton to a friend, in which Payton said he imagined himself killing those around him and then turning a gun on himself.