Green's family posted a message Friday on the Cardinals website' announcing the death.
''His family was by his side and he fought hard,'' the statement said. It did not disclose other details, though the Cardinals said Green had died of a heart attack.
Green was the first black head coach in Big Ten history when he took over at Northwestern in 1981 and was just the third black head coach in the NFL when the Vikings hired him in 1992. Through it all, Green worked hard to provide opportunities for minorities on his coaching staffs and was beloved by his players for the loyalty he showed them.
''He was one of the forerunners, standard bearers from an African-American standpoint,'' Vikings COO Kevin Warren said. ''He was there early and won a lot of football games. He not only got in that position as a head coach, he then hired people and gave them opportunities.''
Green spent 10 seasons in Minnesota, leading the Vikings to eight playoff appearances and two NFC championship games. He had only one losing season and compiled an overall record of 97-62, a mark second only to Bud Grant in franchise history. That included a 15-1 regular season in 1998 spearheaded by a record-setting offense.
''They were pretty good when he was here,'' current Vikings coach Mike Zimmer said. ''I'm just trying to get close to him.''
Green went out on a limb in the draft before that season, taking Randy Moss at No. 21 after the super-talented receiver fell due to character concerns. Moss was a sensation from the start, teaming with Cris Carter, Jake Reed, Randall Cunningham and Robert Smith to give the Vikings the most dynamic and explosive offense the league had ever seen. The Vikings scored a record 556 points that season, a mark that stood until New England broke it in 2007.
Green went 4-8 in the postseason, one of the reasons he was fired by Minnesota late in the 2001 season.
''Denny made his mark in ways far beyond being an outstanding football coach,'' the Vikings said. ''He mentored countless players and served as a father figure for the men he coached. Denny founded the Vikings Community Tuesday Program, a critical initiative that is now implemented across the entire NFL. He took great pride in helping assistant coaches advance their careers. His tenure as one of the first African American head coaches in both college and the NFL was also transformative. Our thoughts and prayers are with the entire Green family.''
Smith tweeted: ''Rest in peace Denny. I lost my mother in April, I feel like I just lost father.''
Green's leadership was never needed more than during training camp in 2001 when offensive tackle Korey Stringer collapsed and died from heat illness, but his tenure in Minnesota also was marked by controversy.
He penned a book in 1997 entitled ''No Room for Crybabies'' in which he threatened to sue the ownership group if he didn't obtain an ownership stake. And at the end of the 2001 season, he was ousted with one game left in the season after losing a power struggle with owner Red McCombs.
Green finished his three years in Arizona with a 16-32 record. Perhaps his biggest accomplishment with the Cardinals was overseeing the drafting of Larry Fitzgerald as the No. 3 overall pick in 2004. Fitzgerald was a ball boy for Green's Vikings.
Of course, many remember Green's final season in Arizona in 2006 for a Monday night loss to Chicago, when the Bears returned two late fumbles and a punt for touchdowns to rally from a 20-point deficit. Afterward, in one of the more memorable postgame rants by an NFL coach, Green pounded the podium and yelled, ''The Bears are who we thought they were!'' afterward, a line that would be replayed endlessly over the years.
Green was well known for his ''Denny-isms,'' unique phrases like ''Plan your work and work your plan,'' which he would often say during practice.
''I still use that `Denny-ism' today,'' Raiders coach Jack Del Rio said. ''Coach Green is going to be missed dearly by everyone that was lucky enough to know him.''
Green was also an avid drummer, and Moss said on ESPN's ''NFL Live'' that ''we had a team and one thing he taught us was to play to one beat. His legacy will live on.''
Born Feb. 17, 1949, in Harrisburg, Pennsylvania, Green once said he was struck by watching early Big Ten football games and seeing both Minnesota and Iowa putting together successful seasons behind black quarterbacks. Green enrolled at Iowa, too, and played running back for the Hawkeyes from 1968-70. He played for the BC Lions in Canada in 1971 before returning to coach in college, beginning at Dayton in 1973 and gradually climbing to bigger programs. Green was also a head coach at Stanford and served as an assistant to Bill Walsh on the dominant 49ers teams of the 1980s.
''All of us at the Cardinals are incredibly saddened by the news of Dennis Green's passing,'' Cardinals President Michael Bidwell said. ''Coach Green will rightly be remembered as a true innovator, leader and pioneer among football coaches. We express our deepest sympathy to his family and his many friends.''
The family asked that in lieu of flowers, contributions be made to the Boys and Girls Club of San Diego.
''He did so much for me,'' tweeted former coach Tony Dungy, who was a defensive coordinator under Green with the Vikings. ''Was looking forward to saying thanks at HOF. Tomorrow not promised.''
AP NFL website: www.pro32.ap.org and www.twitter.com/AP-NFL
AP Sports Writer Bob Baum in Phoenix contributed to this report.