MIAMI — 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.

Bruce Bobbins, a spokesman for the Buoniconti family, said he died Tuesday in Bridgehampton, New York. A cause of death was not immediately known.

Buoniconti was bypassed in the NFL draft but went on to a 15-year career. He helped the Dolphins win back-to-back Super Bowls, including the 1972 team that finished 17-0.

Following retirement, Buoniconti and his son, Marc, worked to raise more than a half-billion dollars in the search for a cure for paralysis. The younger Buoniconti was paralyzed from the shoulders down making a tackle for The Citadel in 1985.

Marc Buoniconti said his father was his biggest hero.

“He could have been sitting on the beach sipping champagne for the rest of his life,” the younger Buoniconti said in 2017. “But what did he do? He went around and gave the rest of his life to help his son.”

Nick Buoniconti was chosen for the all-time AFL team in 1970. He was chosen for the NFL Pro Bowl in 1972 and 1973.

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. In recent years he struggled with symptoms of CTE, a degenerative brain disease associated with repeated blows to the head.

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

He 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 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 inducted into the Hall of Fame in 2001.

In 1985, he and Marc Buoniconti helped to found the Miami Project to Cure Paralysis, which has become the world’s largest spinal cord injury research center.