For his forthcoming book "Monsters: The 1985 Chicago Bears and the Wild Heart of Football," author Rich Cohen caught up with former Bears coaches and players to find out what made the most fearsome team in NFL history tick. In this excerpt, he explores the team's rise and the stormy relationship between coach Mike Ditka and assistant Buddy Ryan, the brains behind the Bears' intimidating defense.

For Mike Ditka, it must have been maddening. He was the coach of the Chicago Bears but had little control over the defense—he...