NBA and Civil Rights Icon Bill Russell Dead at 88: 'Our Beloved No. 6'

Bill Russell, the towering NBA legend in a league of his own, has died. He was 88.

According to a statement posted on his official Twitter account Sunday, Russell "passed away peacefully" with his wife Jeannine by his side.

The statement added that "arrangements for his memorial service will be announced soon" and "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 statement concluded. "And we hope each of us can find a new way to act or speak up with Bill's uncompromising, dignified and always constructive commitment to principle. That would be one last, and lasting, win for our beloved #6."

A cause of death was not disclosed. Russell's reps did not immediately return PEOPLE's request for comment.

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Born in 1934 in West Monroe, Louisana, William Felton Russell later joined the basketball team at McClymonds High School in Oakland after moving to Northern California with his family, according to a biography of Russell on the NBA's website.

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His performance there earned him a scholarship to attend the University of San Francisco, where the 6-foot-9 Russell helped the team earn 56 straight victories and two NCAA titles in 1955 and 1956.

Russell was selected by the St. Louis Hawks with the second overall pick in the 1956 NBA Draft but was traded to the Boston Celtics the same day. The partnership would prove a fruitful one — together with head coach Red Auerbach, the Celtics won 11 championships during Russell's tenure.

Eight of those titles came consecutively from 1959 to 1966, a feat that has not been replicated again in the NBA or the other major American sports leagues.

"There are two types of superstars," former Celtics player Don Nelson once told the Boston Herald, according to NBA.com.

"One makes himself look good at the expense of the other guys on the floor," Nelson continued. "But there's another type who makes the players around him look better than they are, and that's the type Russell was."

Russell was also active in the Civil Rights Movement, having boycotted an NBA game in 1961 after a restaurant in Kentucky refused to seat him and his Black teammates, author Doug Merlino wrote in his book, The Crossover: A Brief History of Basketball and Race, from James Naismith to LeBron James.

After civil rights leader Medgar Evers was assassinated in Jackson, Mississippi in 1963, Russell held the city's first integrated basketball camps.

In one touching moment in 1959, Russell visited the African country of Liberia, where he spoke to a group of young students. One of them, Merlino wrote, asked Russell why he was visiting the country, and he responded by explaining, "I came here because I believe that somewhere in Africa is my ancestral home. ... I came here because I am drawn here, like any man, drawn to seek the land of my ancestors."

The students all stood up and cheered at his response, Merlino wrote.

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Russell was awarded the Presidential Medal of Freedom by then-President Barack Obama in 2011.

"More than any athlete of his era, Bill Russell came to define the word winner," Obama said at the presentation ceremony, according to NPR.

Russell never defined himself as a "basketball player," the former president continued, but as someone who plays basketball.

"Bill Russell the man," Obama added, "is someone who stood up for the rights and dignity of all men."