Let's get the obvious out of the way. Bill Belichick is probably the greatest NFL head coach of all time. Belichick harnessed his coaching prowess as defensive coordinator under Bill Parcells with the Giants, winning the Super Bowl in 1986 and 1990. After a forgettable tenure as head coach with the Cleveland Browns, Belichick followed Parcells to the New England Patriots where he would soon become head coach in 2000 and become a record breaker and dynasty maker. With five Super Bowl wins and seven AFC championships, Belichick is a skilled tactician, confusing defenses for two decades with a creative playbook.
Don Shula was the only coach to have a perfect season, remaining undefeated throughout the season and the playoffs, winning the Super Bowl with the Miami Dolphins in 1972. Shula led the Dolphins to another Super Bowl victory in 1973, later becoming the highest-winning coach in the NFL with 347 career wins. The fact that Shula still had winning seasons during both the Dead Ball Era in the 70s and the offensive turnaround in the 80s speaks volumes.
After beginning his career with an 18-46 record in five seasons with the newly introduced Dallas Cowboys, Landry led the Cowboys to two decades of success. In addition to his strong defenses, Landry was known for inventing the 4-3 defensive background, bringing the shotgun formation and pre-snap motions to the offense. Landry would cement himself as one of the greatest NFL head coaches, leading the Cowboys to Super Bowl victories in 1971 and 1977.
When Bill Parcells became head coach of the New York Giants, they had just one winning season in the past ten years. After finishing to a disastrous 3-12-1 season in 1983, the Giants bounced back the following seasons with a 9-7 and 10-6 record. Parcells then led the Giants to their first Super Bowl victory in 1987 against the Denver Broncos. Parcells later had success coaching the Jets, Patriots, and Cowboys.