Bill Russell, the National Basketball Association (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 U.S. 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.

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 and an archetype of selflessness who won with defense 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.

The battles on the court between the centers were fierce — signature showdowns in the NBA. Russell led the University of San Francisco to NCAA championships in 1955 and 1956 and won a gold medal at the 1956 Olympics.

In Boston, Russell left a lasting mark as a Black athlete in a city — and country — where race is often a flash point. In 2011, President Barack Obama awarded Russell the Medal of Freedom. Two years later, a statue of Russell was unveiled on Boston’s City Hall Plaza.