Butkus (Chicago Bears) and Nitschke (Green Bay Packers) both have numerous Pro-Bowl Selections and built their teams defense with their talent and toughness on the field. They made numerous interceptions and were among the most feared tacklers.
Butkus had a reputation of being mean. Someone said, "The main differences between Nitschke and Butkus are that Nitschke would tear your head off, whereas Butkus would tear your head off, then eat it." These two definitely helped to escalate the great rivalry between the Bears and Green Bay.