Dan Rooney, the longtime Pittsburgh Steelers chairman who helped shape the modern National Football League and was one of the last surviving links to its founders, died on Thursday in Pittsburgh. He was 84.

The Steelers announced his death on their website.

“My father meant so much to all of us, and so much to so many past and present members of the Steelers organization,” said Mr. Rooney’s son, the team president Arthur Rooney II. “He gave his heart and soul to the Steelers, the National Football League and the City of Pittsburgh.”

Mr. Rooney’s health had deteriorated in recent weeks, and he had uncharacteristically missed the league’s annual meeting in Phoenix in late March. In a speech there to the other team owners, Commissioner Roger Goodell praised Mr. Rooney for his decades of service, and flew to Pittsburgh to see him soon after the meeting concluded.

Except for a stint as ambassador to Ireland in the Obama administration, Mr. Rooney was part of the Steelers almost from birth, having been born the year before his father, Art, bought the team in 1933.