*It’s always surprising to learn about superstars who’ve flaunted in public the image of a hero, but turn out being monsters behind closed doors.

According to a new book “Sweetness: The Enigmatic Life of Walter Payton,” the Chicago Bears legendary running back abused painkillers in his retirement, eventually becoming suicidal.

According to the book, written by Jeff Pearlman, Payton mixed Tylenol and Vicodin and kept tanks of nitrous oxide in his garage. At one point he got a hold of Ritalin from a friend whose son was prescribed the drug.

An excerpt of “Sweetness: The Enigmatic Life of Walter Payton,” by Jeff Pearlman, will appear in the Oct. 3 issue of Sports Illustrated, 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.

The book further delves into the details of his extramarital affairs. During his induction into the Hall of Fame, both his wife and mistress attended, obligating Payton’s personal assistant, Ginny Quirk, to baby sit the grown women and keep them from basically killing each other.

The football player’s life came to an abrupt halt when he became deathly ill from a rare liver disease and bile duct cancer. He died in 1999.

“Sweetness: The Enigmatic Life of Walter Payton” will be released Oct. 4.