A statement posted to his Twitter account said he passed away peacefully with his wife Jeannine by his side.

Other statements about him did not hold back the accolades.

NBA Commissioner Adam Silver said, "Bill Russell was the greatest champion in all of team sports."

A statement from the Celtics read, "To be the greatest champion in your sport, to revolutionize the way the game is played, and to be a societal leader all at once seems unthinkable, but that is who Bill Russell was."

And Magic Johnson tweeted he was "heartbroken," to learn of Russell's death.

It is hard to understate Russell's impact on the sport and its players.

Here's how NBA legend Kareem Abdul-Jabar described Russell ahead of an awards ceremony in 2017:

"Well, you know, he's one of my heroes, someone who helped me learn the game. If I hadn't had the opportunity to watch him I wouldn't have learned how to play the game as well as I did. So I feel that I owe him a lot."

Russell became a superstar in the 1950s and '60s not with flashy scoring plays but through dominating rebounding and intense defensive play that reshaped the game.

The Celtics won 11 NBA titles in Russell's 13 years with the team from 1956 through 1969.

Off the court, Russell was opinionated and complicated. Russell often criticized Boston, a city with a history of racial strife, and was one of the sports world's leading civil rights activists.

He was in the front row in Washington in 1963 when Dr. Martin Luther King delivered his "I Have a Dream" speech.

Russell had a famous but friendly rivalry with fellow athlete Wilt Chamberlain. In 1965, Chamberlain became the first NBA player to earn a $100,000 annual salary so Russell demanded - and got - a contract from the Celtics that paid him $100,001.

After retiring from play, Russell returned to basketball as general manager and coach of the Seattle SuperSonics, and later as coach of the Sacramento Kings.

In 2011, President Barack Obama cited Russell's dedication to mentoring when he awarded him the Presidential Medal of Freedom.

On Sunday, the 44th president tweeted, "Today we lost a giant. As tall as Bill Russell stood, his legacy rises far higher - both as a player and as a person."