John Thompson Jr., who died Sunday night at 78, was a towering presence in college basketball, both in physical stature and impact on the court. Most important, according to esteemed peers who reflected on the legacy of the former Georgetown coach, he was an uncompromising advocate for social justice well ahead of his time.

His death led some of the sport’s most accomplished figures to speak reverentially about the first African American coach to win a national championship, deploying a roster consisting of all Black players.

Thompson had been dealing with health issues for months, family and friends said, but no cause of death has been provided.

“It’s too bad he’s not in this time right now,” said Syracuse Coach Jim Boeheim, a longtime foil for Thompson before the Naismith Memorial Basketball Hall of Famers forged a close friendship following years of acrimony. “We could use a John Thompson right now.”

Few coaches have been linked with Thompson more than Boeheim and Lou Carnesecca, the legendary former St. John’s coach who recalled coming to the District in the late 1950s as an assistant coach to recruit the 6-foot-10 center from Archbishop Carroll High.

Georgetown’s games against St. John’s, Syracuse and Villanova helped elevate the profile of the original Big East, turning it into perhaps the premier college basketball conference in the country. In 1985, the Hoyas, Wildcats and Redmen (later renamed the Red Storm) reached the Final Four. No conference since has sent that many teams to the Final Four.

“I spoke to his mother about St. John’s, about playing in the Garden, etc., etc.,” Carnesecca, 95, who retired from coaching in 1992, said during a telephone interview. “She said, ‘No, I’m not going to send my boy to New York.’ I said: ‘He’s 6-foot-9. Who’s going to go after him?’ ”

Thompson would go on to command center stage regularly during the Big East tournament at Madison Square Garden during the most prosperous years of the conference, when Georgetown resonated nationally and transcended college basketball.

The Hoyas brand became part of hip-hop culture, with artists such as Ice Cube wearing Georgetown gear. In 2012, D.C.-based rapper Wale released the song “Georgetown Press.”

“He was a coach fans went to see,” Boeheim said of Thompson, who delivered Georgetown the NCAA title in 1984. “Fans don’t go to see coaches. They don’t. Fans went to see Georgetown because they were great teams, but they went because John Thompson was there on the sideline. That was a big, big part of it. He sold out every arena he went to.”

Thompson’s feuds with Boeheim became as heated as the play on the court, with Thompson famously declaring Manley Field House officially closed when the Hoyas won the final game at the school’s former home court before Syracuse moved to the Carrier Dome.

Boeheim, now 75, was in his 13th season at Syracuse when Thompson famously walked off the court at Capital Centre, Georgetown’s since-demolished home arena in Landover, to protest an NCAA policy prohibiting freshmen from receiving athletic scholarships if they failed to meet certain academic markers.

Thompson at the time indicated his decision to leave the court before the Hoyas tipped off against Boston College came out of frustration that the rule would affect African Americans at a significantly disproportionate rate and that too few in leadership positions realized its implications.

“That’s the part that I kind of see the most. He stood up. I watched the game when he walked off, and I kind of said, ‘Good for him,’ ” Michigan State Coach Tom Izzo said. “It was something he believed in, and I think it was unfair then, not just racially but socioeconomically. He stood by himself, and I think he was big and strong and tough enough to do it.”

“It was the first time I’d noticed a coach taking the lead to fight against injustice,” George Mason Coach Dave Paulsen said in a statement. “It’s fitting that this past week NBA players — many years later — followed his lead in walking off the court. Coach Thompson’s ability to coach at the highest level while pursuing social change was an inspiration to coaches at all levels of the game.”

Thompson also welcomed Allen Iverson to Georgetown when other schools dropped their recruitment following his involvement in a brawl in a bowling alley in 1993. Iverson, who said at the time that someone called him the n-word, was accused of hurting three people with a chair, resulting in convictions on three felony counts of maiming by mob.

Two years later, while Iverson was playing for Thompson, an appeals court overturned the convictions. The No. 1 pick in the 1996 NBA draft and a Naismith Hall of Famer credited Thompson for saving his life in an emotional speech during his induction ceremony.

“I’m going to miss you, but I’m sure that you are looking down on us with a big smile. I would give anything just for one more phone call from you only to hear you say, ‘Hey, [expletive],’ then we would talk about everything except basketball,” Iverson wrote Monday on Twitter.

Michael Jordan said in a statement that he “admired” and “loved him dearly.” “Coach Thompson was truly a great man and a legend in college basketball. He had such a profound impact on his players and was a father figure to so many of them.”

“It goes without saying that, I don’t know, somebody could research I’m sure, but I don’t think there were many African American head coaches in 1972 when he started,” Boeheim said. “Well, there’s a lot more today, and they’re because of John Thompson.”

One of the most prominent active Black coaches in men’s college basketball is Florida State’s Leonard Hamilton, who coached the Washington Wizards in 2000-01, two seasons after Thompson resigned from Georgetown.

Hamilton called Thompson a “father figure” who affected him immeasurably, particularly as the two grew closer over the past several decades.

“There’s absolutely no doubt about it that the Black coaches who are coaching today, we all stand on John Thompson’s shoulders,” Hamilton said. “There’s no question that he set the table. He opened up the eyes of America to show people that not only can we play, but we can also lead from an administrative, coaching standpoint.”

Outside of the Big East coaching ranks, Thompson had a long-standing kinship with Dean Smith, the legendary former coach at North Carolina who died in 2015. Thompson arrived roughly two hours before the funeral and sat alone in a church pew, a visual current Tar Heels coach Roy Williams recalls vividly.

As an assistant to Smith from 1978 to 1988, Williams watched the bond between the fierce adversaries on the court flourish into a personal relationship filled with mutual respect and unbroken trust.

Among the most indelible images in the sport’s history are those of Thompson and Smith embracing, as they did following North Carolina’s 63-62 win over the Hoyas in the 1982 national championship game.

“I considered him a mentor,” Williams said of Thompson. “There’s no question almost everything you see me do I learned from Coach Smith, but there were three other guys — Bob Knight, Jerry Tarkanian and John Thompson. And I loved John Thompson.

“I loved him as a person. I loved him as a basketball coach. We lost a true giant in our game.”

For aspiring coaches, he was a resource. Former NBA coach David Fizdale told The Post: “Everyone wanted to play for him. Coaches wanted to coach like him. He always had time for a young coach, and that meant a lot to me. He was a great coach who showed young Black coaches that it was possible, and he always kept it real with you.”

Gary Williams, Maryland’s former coach, also coached Boston College in the Big East against Thompson from 1982 to 1986.

“The time he was in, how hard it must have been to do what he said, to say what he said,” Williams said, adding Thompson was outspoken about the dearth of Black officials in the Big East. “He had things that were very controversial back then, but he was never afraid if he thought in his mind he was helping the situation.

“John was very vocal about the opportunities for young Black coaches to become assistants at major college programs, which hopefully would lead to head coaching positions. He was not afraid to say that, and really back then, beside Nolan Richardson and John Chaney, [Thompson] was the guy.

“I remember there in the ’80s, Georgetown was, gear-wise, every kid you saw had some Georgetown stuff on. I guess they and Michigan were the ones that kind of took over when you looked down at crowds at games and stuff like that. Whether Georgetown was playing or not, there was always Georgetown stuff.”

Thompson’s influence extended to Maryland football coach Michael Locksley, who tweeted that the former Georgetown coach was “my first vision of what I could become. A man that fought for Minority Coaches of all sports as one of the original founders of the [Black Coaches Association]. The first African American head coach to win an NCAA Championship. Always protected his team from the streets. More than a Coach!! Rest in Power Big Coach.”

The legacy he leaves is one of activism.

“In honor of John Thompson, it should motivate us to continue to keep fighting for what we believe is right,” Hamilton said. “I’m going to be even more motivated now, for how much he meant to me, to continue to keep trying to do the things that emulate the success that he had and the philosophies that he had. But more than anything else, I want to continue to stand up and use our platform for what is right in our society.”

Kareem Copeland contributed to this report.

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