Butler is best known for helping to assemble the Buffalo Bills, who went to four straight Super Bowls from 1990-93. He left the Bills to become general manager of the Chargers in January 2001.
"It's hard to put into words this feeling of loss. We'll miss him," said Chargers President Dean Spanos. "John was a man's man and someone I admired very much. All of our thoughts and prayers right now are with his wife, Alice, and daughter, Andrea. He meant so much to everyone here. It's hard to put into words this feeling of loss. We'll miss him."
Since rejoining the Chargers, Butler was instrumental in restoring their roster to playoff caliber. He helped bring in a host of bright, young players through the draft, including Pro Bowl running back LaDainian Tomlinson, quarterback Drew Brees, cornerback Quentin Jammer, linebacker Ben Leber, guard Toniu Fonoti, and wide receiver Reche Caldwell.
Taking over in San Diego after the Chargers finished 1-15 in 2000, Butler immediately made dramatic improvements.
Those selections, along with Butler's signings of linebacker Donnie Edwards in 2002, and defensive end Marcellus Wiley and cornerback Ryan McNeil in 2001, helped the Chargers improve to 8-8 last season.
Butler was equally adept at finding quality players through free agency.
Over the past three offseasons, he signed six Pro Bowl players through free agency, including wide receiver David Boston and fullback Lorenzo Neal this year, linebacker Donnie Edwards and tight end Stephen Alexander in 2002, and defensive end Marcellus Wiley and defensive back Ryan McNeil in 2001.
"He knew what it takes to win in this league," said Assistant General Manager A.J. Smith. "Professionally, we've lost the best there is. Personally, I've lost my best friend."
Butler's tenure in the NFL spanned 18 seasons, including four with the Chargers and 14 with Buffalo from 1987-2000, where he had a hand in making the Bills one of the NFL's most-successful teams of the 1990s.