NBA great Bill Russell, the cornerstone of a Boston Celtics dynasty that won 11 titles and a powerful voice for social justice, has died at the age of 88, his family said Sunday.

"Bill Russell, the most prolific winner in American sports history, passed away peacefully today at age 88, with his wife, Jeannine, by his side," said a statement posted on social media.

Russell's 11 titles with the Celtics included eight in a row from 1959-1966. Today's NBA Finals MVP award is named for him.

He averaged 15.1 points and 22.5 rebounds per game for his career, building a famed rivalry with Wilt Chamberlain in the 1960s.

He would become the first Black coach in the NBA and the first Black player inducted into the Basketball Hall of Fame in 1975.

Off the court Russell was a giant in the fight for civil rights, receiving the Presidential Medal of Freedom, the United States' highest civilian honor, from President Barack Obama in 2011.

"Today, we lost a giant," Obama said in a statement on Twitter. "As tall as Bill Russell stood, his legacy rises far higher -- both as a player and as a person.

"Perhaps more than anyone else, Bill knew what it took to win and what it took to lead. On the court, he was the greatest champion in basketball history. Off of it, he was a civil rights trailblazer, marching with Dr. King and standing with Muhammad Ali.

"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."

Russell's family said his "understanding of the struggle is what illuminated his life."

"Bill called out injustice with an unforgiving candor that he intended would disrupt the status quo, and with a powerful example that, though never his humble intention, will forever inspire teamwork, selflessness and thoughtful change."

NBA Commissioner Adam Silver called Russell "the greatest champion in all of team sports," but added that his accolades "only begin to tell the story of Bill's immense impact on our league and broader society.

"Bill stood for something much bigger than sports: the values of equality, respect and inclusion that he stamped into the DNA of our league," Silver said in a statement on Sunday.

Those beliefs, more than his prowess on the court, were what inspired Magic Johnson's love of Russell, the Lakers legend said on Sunday as he joined in an outpouring of tributes.

"He was one of the first athletes on the front line fighting for social justice, equity, equality, and civil rights," Johnson said in a statement on Twitter.

"That's why I admired and loved him so much. Over the course of our friendship, he always reminded me about making things better in the Black community."

Current Celtics stars Jayson Tatum and Jaylen remembered the franchise legend, the club saying in a statement that "Bill Russell's DNA is woven through every element of the Celtics organization."

Michael Jordan, who for many inherited the mantle of greatest ever NBA player from Russell, said Russell "paved the way and set an example for every Black player who came into the league after him, including me.

"The world has lost a legend," Jordan said, a comment echoed by former New York Knicks great Patrick Ewing.

Former tennis great and women's rights activist Billie Jean King said Russell had a "huge influence" on her career.

"He was the ultimate leader, ultimate team player & ultimate champion," King said. (AFP)