A Pro Football Hall of Fame offensive tackle for 16 seasons in the National Football League (NFL), he was a part of six NFL championships, five of them with the Green Bay Packers before closing out his tenure with the Dallas Cowboys with a win in Super Bowl VI.

[1][3] Playing on both the offensive and defensive line at SMU, Gregg earned All-Southwest Conference honors in his final two seasons.

[4] Gregg was a key player in the Packers dynasty of head coach Vince Lombardi that won five NFL championships and the first two Super Bowls.

They both helped the Cowboys win Super Bowl VI in January 1972, making them the only players (along with former teammate Fuzzy Thurston, who was on the Baltimore Colts NFL championship team in 1958 and Tom Brady of the New England Patriots and Tampa Bay Buccaneers) in professional football history to play on six NFL title teams.

but official Packers team historian Cliff Christl can find no evidence of Lombardi ever saying or writing that.

[7] In 1999, he was ranked 28th on The Sporting News list of the 100 Greatest Football Players, putting him second behind Ray Nitschke among players coached by Lombardi, second behind Anthony Muñoz (whom he coached) among offensive tackles, and fourth behind Munoz, John Hannah, and Jim Parker among all offensive linemen.

[11] Darden has explained that the 1977 Cleveland Browns did not respond to Gregg's coaching style, which contributed to his firing with one game remaining.

[16] When his longtime former teammate Bart Starr was fired after nine years as head coach of the Packers in December 1983, Gregg was allowed out of his Bengals' contract to take over in Green Bay.

[21] Gregg knew that any new coach would be essentially rebuilding the program from scratch, but when acting president William Stalcup asked him to return, he felt he could not refuse.

The team was so short on offensive linemen that Gregg had to make several wide receivers bulk up and switch to the line.

In a 2012 interview with The New York Times, he said the players on the two teams he coached should have had their numbers retired for restoring dignity to the program.

In October 2011, he was diagnosed with Parkinson's disease, thought to be caused by concussions from playing over two decades of high school, college, and professional football.

[1][32] In addition to his wife, he was survived by a son, Forrest Jr.; a daughter, Karen Gregg Spehar; and several siblings.