Walter Payton, who was indisputably one of the greatest running backs in the history of the NFL, died in 1999 at the age of 45 from bile duct cancer. A new biography by Jeff Pearlman called Sweetness: The Enigmatic Life of Walter Payton that comes out officially in October makes the great Payton seem like a common depressive, in an admirable hero, a heartless adulterer, a terrible father as well as a great father–all in one book.

In an excerpt released on SportsIllustrated.com, which you can read here, Pearlman talks about Payton’s infidelity, drug abuse, his fantastic appreciation for his fans, his devotion to his kids, and his heart-wrenching struggle with cancer. Pearlman realized before publishing that this book wasn’t all pretty.

In an interview with Sports Illustrated, to which he contributes as a writer, he said, “It hurts me that this will hurt his kids. It does because Jarrett and Brittney are wonderful, engaging, fun, caring people and they’re uplifting figures in the Chicago landscape. That said, I set out to write a definitive biography — period. When people would ask, ‘Well, is this going to be positive?’ I’d say, ‘Not positive, not negative — definitive.’ ”

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