Pro Football Hall of Fame middle linebacker Nick Buoniconti, an undersized overachiever who helped lead the Miami Dolphins to the NFL’s only perfect season, has died at the age of 78.

“Today, with a heavy heart and profound sorrow, my family and the entire Miami Project to Cure Paralysis and Buoniconti Fund community mourn the loss of a man who was truly larger than life, my father, NFL Hall of Famer Nick Buoniconti,” Marc Buoniconti said in a statement. “My dad has been my hero and represents what I have always aspired to be: a leader, a mentor and a champion.

Family spokesman Bruce Bobbins said Nick Buoniconti died Tuesday in Bridgehampton, New York. A cause of death wasn’t immediately known.

A native of Springfield, Massachusetts, Buoniconti played guard on offense and linebacker on defense for Notre Dame. But at 5-foot-11 and 220 pounds, he was small for an NFL linebacker.

Buoniconti was taken in the 13th round by the Boston Patriots of the upstart AFL and played for them from 1962 to 1968. He made the AFL All-Star Game six times and had 24 career interceptions for the Patriots, including three in a single game in 1968.

Buoniconti played for the Miami Dolphins from 1969 to 1974 and in 1976. He was the leader of Miami’s famed “No-Name Defense,” and in 1973 he set a team record with 162 tackles.

He was an eight-time Pro Bowler and won Super Bowl titles with the Dolphins in 1972, for a team that finished 17-0, and 1973. He was inducted into the Hall of Fame in 2001.

He said in November 2017 that he would donate his brain for CTE research. He revealed in May of that year that he was suffering from memory loss and could not use his left hand, among other ailments.

After his son Marc was paralyzed at age 19 while playing football, Buoniconti was a driving force behind the Miami Project to Cure Paralysis, raising hundreds of millions of dollars for research. Nick and Marc were on a Wheaties box in 1997 as part of the Miami Project.

“He selflessly gave all to football, to his family and to those who are less fortunate,” Marc Buoniconti said in his statement. “He made a promise to me that turned into a revolution in paralysis research. We can best honor his dedication and endless commitment by continuing with our work until that promise is fulfilled and a cure is found,”

Nick Buoniconti also had a successful post-football career in broadcasting and business.

Following retirement, Buoniconti worked as an attorney, as president of U.S. Tobacco and as an agent to such athletes as Bucky Dent and Andre Dawson.

The Associated Press contributed to this report.