The world didn't just lose its greatest sports champion and a civil rights leader on Sunday, when Boston Celtics legend Bill Russell died at age 88. We lost a touchstone to our history that can never be replaced.

The NBA is different from most institutions in how it embraces the greats who built it. Only Pete Maravich had passed when the league honored its 50th Anniversary Team in 1997, and 47 attended the ceremony. Forty-five of the 61 living members were present for the 75th Anniversary Team celebration in February, two years into a global pandemic. These giants are among us, and we don't appreciate them nearly enough.

Russell was singular. He entered the NBA in 1956 and won 11 of the next 13 championships. He was the league's first Black superstar and the first Black head coach of any professional team in North America. He was a childhood friend of Johnny Mathis, a guest of Dr. Martin Luther King Jr. at the March on Washington and a pallbearer at Jackie Robinson's funeral. He attended the Cleveland Summit in support of Muhammad Ali's 1967 Vietnam War protest and earned the Presidential Medal of Freedom from Barack Obama in 2011.

And he was here just yesterday, living long enough to see his life's work come full circle. The same city that rained racism upon him during his playing career showered him with standing ovations some 50 years later.

"Today, we lost a giant," Obama wrote in a Twitter tribute on Sunday. The nation's first Black president added, "For decades, Bill endured insults and vandalism, but never let it stop him from speaking up for what’s right. I learned so much from the way he played, the way he coached, and the way he lived his life."

A statue of Russell now sits outside Boston City Hall, steps from where civil rights attorney Ted Landsmark was nearly killed by a group of white teenagers protesting the city's first attempt to desegregate its schools. He only accepted the honor when the Celtics agreed to fund an annual grant for local mentoring programs.

"There are no other people's children in the United States," the statue's inscription reads, echoing words of mentorship wisdom he wrote for the Harvard Business Review. "There are only next-generation Americans."

Few did more for their generation than Russell, whose public life spanned 13 American presidents from Dwight Eisenhower to Joe Biden, and we are better for it. Imagine our impact if we could ever approach it.

The NBA named its Finals MVP award for Russell in 2009, and he was on hand to present it every year until 2019, when fears of COVID-19 limited him to congratulating annual winners in videos he posted to Twitter.

His relationships extended to 2022 recipient Stephen Curry, among the privileged few who Russell roasted and reminded, "I only give the guys I really like a hard time." When Kareem Abdul-Jabbar, David Robinson, Dikembe Mutombo, Alonzo Mourning and Shaquille O'Neal presented him with the NBA's inaugural lifetime achievement award in 2017, Russell pointed to each of the five centers whose careers spanned the first 42 years from his retirement and told them through that unforgettable cackling laugh, "I would kick your ass."

Russell once gave Charles Barkley the middle finger on live television and warned Michael Jordan during a round of golf, "I don’t think you will live long enough" to break his records of 11 titles and eight straight.

What makes the NBA so special are these bonds forged across generations, all of which have members still with us. Bob Pettit, at 89 years old, attended the 75th Anniversary Team commemoration in Cleveland.

"Let me tell you, anybody who says it isn’t nice to be remembered is lying," Pettit, still a New Orleans Pelicans season-ticket holder, told NBA.com's Steve Aschburner. "It is very nice. So I am very pleased to be one of the 75, as I was pleased to be one of the 25 and one of the 50. I may not be around for 100."

Kevin Garnett, who Russell once told, "I couldn't be more proud of you than I am of my own kids," says "everyone has a vet" — someone who takes you under his wing until you're ready to fly on your own. Sam Mitchell was his. He was Rajon Rondo's. Rondo is Darius Garland's. Four players, 33 years and counting. The league is now working on a ninth decade of mentorship, and Russell was the greatest of them all.

That Russell was in our lives until Sunday is a reminder of how relatively young the NBA is and how fresh some of the scars of its past still are. Russell led a walkout when, in 1961, a Kentucky restaurant told his Celtics teammates Sam Jones and Satch Sanders, "We really can’t serve you people." Half a century later, Russell was kneeling in support of one-time Super Bowl starting quarterback Colin Kaepernick when the nation's sitting president was still imploring NFL owners to "get that son of a bitch off the field right now."

When Giannis Antetokounmpo and the Milwaukee Bucks elected to sit out Game 5 of their first-round playoff series in protest of the August 2020 shooting of Jacob Blake, Russell was there to support them.

Through Russell we could see our own history, both sordid and splendid. He was the beacon.

You could not see Cy Young sit down with Clayton Kershaw or Georges Vezina hobnob with Marc-Andre Fleury, but Bill Russell befriended every superstar who followed, and they embraced him back. As the NFL, MLB and NHL engage in tumultuous public relationships with legends Tom Brady, Barry Bonds and Wayne Gretzky, Michael Jordan is on the NBA's board of governors, and LeBron James will join him in retirement.

This is why Kobe Bryant's death hit the basketball world so hard two years ago. The Los Angeles Lakers link that connected Abdul-Jabbar, Magic Johnson, O'Neal, Bryant and James over five decades of fandom was broken, and we could never get it back. There will be no 84-year-old Bryant cheering the 2062-63 Lakers on from the sidelines, as Russell did at that age for his Celtics in the 2018 Eastern Conference finals.

The deaths of Len Bias and Reggie Lewis similarly disrupted the torch-passing from Russell, John Havlicek, Dave Cowens and Larry Bird to Paul Pierce and now Jayson Tatum. But Russell bridged them all, much the same way Abdul-Jabbar is still present in our lives and regularly sharing wisdom in a Substack newsletter.

"There is a whole lot more truth and love and respect in my 60-year relationship with Bill Russell that I want to share so the world can know him, not just as one of the greatest basketball players to ever live, but as a man who taught me how to be bigger — as a player and as a man," Abdul-Jabbar wrote on Monday, adding, "He had continued to call me kid since our first meeting when I was 14. I think that was his good-natured way of reminding me that he was there first and I would always be following in his giant steps."

The start of this NBA chain is leaving us now. Until Tommy Heinsohn's death in November 2020, you could still find him before games in TD Garden's media dining area, where he would explain how Russell would have dominated today's NBA. Gone, too, are Sam and K.C. Jones and Havlicek. Only Sanders and Bob Cousy remain among the Hall of Famers who built the Celtics into a dynasty and the NBA into a behemoth.

"Satch always says, 'Don’t look over your shoulder. You’ll see them gaining on you,'" the 93-year-old Cousy old The Boston Globe upon learning of Russell's death. "So I’m more and more aware of that every time the phone rings and I get news like this. But I’m a realist. I’m ready for the big basketball court in the sky."

It's only going to get bigger in the years to come, as we continue to lose these giants among us. Only more reason to appreciate Oscar Robertson, Jerry West and the NBA's touchstones to our history while we can.

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Ben Rohrbach is a staff writer for Yahoo Sports. Have a tip? Email him at rohrbach_ben@yahoo.com or follow him on Twitter! Follow @brohrbach