Patriots owner Robert Kraft shares his fondest memories of Steelers chairman Dan Rooney and says that he and his family have always tried to build the Patriots franchise to resonate with fans just like Rooney did with the Steelers. (1:38)

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

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

"Few men have contributed as much to the National Football League as Dan Rooney," commissioner Roger Goodell said in a statement. "A member of the Pro Football Hall of Fame, he was one of the finest men in the history of our game and it was a privilege to work alongside him for so many years. Dan's dedication to the game, to the players and coaches, to his beloved Pittsburgh, and to Steelers fans everywhere was unparalleled. He was a role model and trusted colleague to commissioners since Bert Bell, countless NFL owners, and so many others in and out of the NFL.

"A voice of reason on a wide range of topics, including diversity and labor relations, Dan always had the league's best interests at heart. For my part, Dan's friendship and counsel were both inspiring and irreplaceable. My heart goes out to Patricia, Art, and the entire Rooney family on the loss of this extraordinary man."

Under Rooney's direction, the Steelers won four championships in six years -- Super Bowls IX, X, XIII and XIV. He also played a large role in assembling the 1974 draft class, considered the greatest class in NFL history, in which the Steelers picked four future Hall of Famers -- Lynn Swann, Jack Lambert, John Stallworth and Mike Webster.

"It is a sad day for my family and me," Steelers president Art Rooney II said in a statement. "My father meant so much to all of us, and so much to so many past and present members of the Steelers organization. He gave his heart and soul to the Steelers, the National Football League and the City of Pittsburgh.

"We will celebrate his life and the many ways he left us in a better place."

Among Rooney's lasting accomplishments was his role in the establishment of the Rooney Rule, which was created in 2003 and requires teams to interview minority candidates for head coaching and senior football operation positions. The rule was named in honor of Rooney, who had served as chairman of the league's diversity committee.

Steelers coach Mike Tomlin said in a statement that he is "forever grateful" Rooney hired him in 2007.

"After every game, win or lose, Mr. Rooney would enter our locker room, look me in my eye and shake my hand along with every player who stepped foot on the field," Tomlin said. "He embodied professionalism and was a man who created a family-like atmosphere that will continue on. Football examples only scratch the surface of how he impacted mine and the countless other lives he touched."

Steelers star wide receiver Antonio Brown said in an Instagram post that Rooney was "one of the most genuine, and humble human beings I've had the pleasure of knowing."

Off the field, Rooney was appointed U.S. ambassador to Ireland in 2009 by President Barack Obama and served until his resignation in 2012. In March 2016, the Jackie Robinson Foundation honored Rooney with its Lifetime Achievement Award.

"Dan Rooney was a great friend of mine,'' Obama said in a statement, "but more importantly, he was a great friend to the people of Pittsburgh, a model citizen, and someone who represented the United States with dignity and grace on the world stage. I knew he'd do a wonderful job when I named him as our United States Ambassador to Ireland, but naturally, he surpassed my high expectations, and I know the people of Ireland think fondly of him today.''

Rooney was born July 20, 1932, in Pittsburgh, to Art Rooney Sr., who founded the Steelers the following year. Dan Rooney played football for North Catholic High School and was named to the 1949 all-Catholic League second team, notably losing the first-team spot to quarterback Johnny Unitas -- whom the Steelers later signed, and cut.

Rooney began working for his father in 1955 after graduating from Duquesne University. He was named president of the Steelers in 1975 and held that position until 2003, when he took on the role of chairman and his son, Art Rooney II, took over the presidency.

"My job is to do what's best for the organization and to make that decision regardless of what the consequences are to me personally," Dan Rooney once said. "I take my position very seriously. What I want is an organization that can be together, one where everybody in the place has the same goal, and that is to win."

Rooney, who was inducted into the Pro Football Hall of Fame in 2000, garnered respect throughout the Steelers organization, from players to coaches to scouts. Key Steelers players routinely reference Rooney's impact on the team.

"I have played with guys that have come from other teams. They look shocked when they see our owners, whether it's Mr. Dan Rooney or Mr. Art Rooney II, walking around the locker room and walking around practice," Steelers quarterback Ben Roethlisberger said in January. "They don't ever see their owners. We see our owners every single day. I think it's just a blessing to know that they care about us, and that's one of the reasons we want to go win."

Former Steelers coach Bill Cowher, currently an NFL analyst with CBS, paid tribute to Dan Rooney with a tweet Thursday.

RIP Dan. My Mentor & friend. Thank you for your Guidance & Wisdom. I came a Young Coach & left a Better Man. Your spirit will live forever. — Bill Cowher (@CowherCBS) April 13, 2017

Rooney remained a fixture in the Steelers facility over the last few years. He had an affinity for St. Vincent College, which has hosted 51 training camps for the Steelers.

Cowboys owner Jerry Jones called it "a sad day for anyone who has had an association with the NFL," noting that Rooney "made all of our lives better."

"He shaped the league with instincts, wisdom and a soft-spoken velvet touch," Jones said. "He was a steward and a guardian for the growth and popularity of the NFL, because he loved the game so much."

A confidant of three commissioners, Rooney played a major role in negotiations with the players' union and in league expansion in 1976 to Seattle and Tampa, Florida. He also was involved in scheduling and realignment decisions.

Former commissioner Paul Tagliabue called Rooney "an extraordinary man of faith, conviction, reason and peace."

"He loved his family, his Steelers and his Pittsburgh," Tagliabue said in a statement. "His values were of America, Ireland and his Church. He was an inspiration to millions throughout America, and in many other lands. He was at home on mean streets, in locker rooms and chapels, with presidents, popes, poets and visionaries. Few have served so many so well. Dan was my mentor, role model, indispensable supporter and great friend during five decades. In the NFL, he is irreplaceable. Our thoughts and prayers are with Patricia and his exceptional family."

Rooney is survived by Patricia, his wife of 65 years, as well as seven children, 20 grandchildren, five great-grandchildren and four brothers.

A viewing for family and friends will be held from 2-7 p.m. Monday at Heinz Field, followed by Rooney's funeral at 11 a.m. Tuesday at St. Paul Cathedral in the city's Oakland section.

ESPN's Jeremy Fowler and The Associated Press contributed to this report.