BOSTON, United States (AP) — Bill Russell, the NBA great who anchored a Boston Celtics dynasty that won 11 championships in 13 years — the last two as the first black head coach in any major US sport — and marched for civil rights with Martin Luther King Jr, died Sunday. He was 88.

His family posted the news on social media, saying Russell died with his wife, Jeannine, by his side. The statement did not give the cause of death, but Russell was not well enough to present the NBA Finals MVP trophy in June due to a long illness.

“Bill’s wife, Jeannine, and his many friends and family thank you for keeping Bill in your prayers. Perhaps you’ll relive one or two of the golden moments he gave us, or recall his trademark laugh as he delighted in explaining the real story behind how those moments unfolded,” the family statement said.

NBA Commissioner Adam Silver said in a statement that Russell was “the greatest champion in all of team sports.”

“Bill stood for something much bigger than sports: the values of equality, respect and inclusion that he stamped into the DNA of our league. At the height of his athletic career, Bill advocated vigorously for civil rights and social justice, a legacy he passed down to generations of NBA players who followed in his footsteps,” Silver said.

A Hall of Famer, five-time Most Valuable Player and 12-time All-Star, Russell in 1980 was voted the greatest player in the NBA history by basketball writers. He remains the sport’s most prolific winner as a player and an archetype of selflessness who won with defence and rebounding while leaving the scoring to others. Often, that meant Wilt Chamberlain, the only player of the era who was a worthy rival for Russell.

But Russell dominated in the only stat he cared about: 11 championships to two.

The native of Louisiana also left a lasting mark as a black athlete in a city — and country — where race is often a flash point. He was at the March on Washington in 1963, when King gave his “I Have a Dream” speech, and he backed Muhammad Ali when the boxer was pilloried for refusing induction into the military draft.