Hull is believed to have suffered a heart attack, The Buffalo (N.Y.) News reported.
In his 11 seasons with the Bills, from 1986 to 1996, Hull played in three Pro Bowls. Hull and quarterback Jim Kelly, who arrived in Buffalo the same day and retired the same year, ran the Bills' no-huddle offense.
In the early 1990s, Buffalo became the only team so far to play in four consecutive Super Bowls and the only team to lose all four.
"Of all 47 years of my coaching career, this was one of the most memorable guys I ever had the honor to coach," Marv Levy said. "I'm so sad to hear it. He was a great leader, certainly. He was as likable a guy as you could meet, family-oriented, a great citizen. I'm stunned."
Hull was a football star at Mississippi State and played with the New Jersey Generals in the short-lived U.S. Football League from 1983 to 1986. After his retirement he ran a cattle farm in Greenwood, Miss., with his wife and two children.
"I enjoy every minute of it," he told the News in 2002. "It's a responsibility I like. My grandfather told me that when you put an animal behind that fence, it's your responsibility. If you can't handle it, cut the wire and it will take care of itself. I love the responsibility. I love everything about it."