Pittsburgh Steelers chairman Dan Rooney, one of the NFL's most influential and popular executives, has died. He was 84.

Steelers spokesman Burt Lauten said Rooney died Thursday. No further details were immediately available.

Buffalo Bills owners Terry and Kim Pegula released the following statement regarding Rooney's death:

"Dan Rooney is one of the true pioneers and pillars of the National Football League and deserves a lot of the credit for the success that our sport has enjoyed for a very long time. On top of that, he was as classy and nice of a man you will ever come across. On behalf of the Buffalo Bills and our great fans in Western New York, we send our condolences to the Pittsburgh Steelers and the Rooney family."

Rooney took over operation of the team in the 1960s from his father, Art, who founded the franchise. From there, Dan Rooney oversaw NFL championships for a team that had never even played in an NFL title game.

He was a powerful force within the league. He helped develop the Rooney Rule under which NFL teams are required to interview minority candidates for coaching and front-office positions. He was a key figure in labor negotiations and league expansion.

He made the Pro Football Hall of Fame in 2000 and also served as the U.S. ambassador to Ireland from 2009-2012.