Nick Buoniconti, an undersized overachiever who became a Hall of Fame middle linebacker, helped lead the Miami Dolphins to the NFL’s only perfect season and became a leader in the effort to cure paralysis, died July 30 in Bridgehampton, N.Y. He was 78.

A family spokesman, Bruce Bobbins, confirmed the death. In recent years, Mr. Buoniconti struggled with symptoms of chronic traumatic encephalopathy, or CTE, a degenerative brain disease associated with repeated blows to the head. He had recently battled pneumonia, Dolphins Senior Vice President Nat Moore said.

The 5-foor-11, 220-pound Mr. Buoniconti was bypassed in the NFL draft but went on to have a 15-year career. He was captain of the Dolphins’ back-to-back Super Bowl champions, including the 1972 team that finished 17-0.

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

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

After his football career, Mr. Buoniconti worked as a lawyer and broadcaster and was president of the U.S. Tobacco Company. He was also an agent to professional athletes, including baseball players Bucky Dent and Andre Dawson. For 23 seasons, he was co-host of the weekly sports show “Inside the NFL” on the HBO cable network.

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

Nicholas Anthony Buoniconti Jr. was born Dec. 15, 1940 in Springfield, Mass. His family ran a bakery.

Mr. Buoniconti played guard on offense and linebacker on defense for the University of Notre Dame, from which he graduated in 1962. Chosen in the 13th round by the Boston Patriots of the upstart American Football League, he played for the Patriots from 1962 to 1968. He made the AFL All-Star Game six times and had 24 interceptions for the Patriots, including three in a single game in 1968.

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

“He was the consummate team captain, the heartbeat of our team,” Hall of Fame fullback Larry Csonka said.

Mr. Buoniconti was inducted into the Pro Football Hall of Fame in 2001.

After taking night classes at Suffolk University in Boston, he received a law degree in 1968.

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.

“Marc, the Miami Project Team and I are committed to carry Nick’s banner and legacy forward to the goal line,” project chairman Barth Green said.

— Associated Press