Bill Russell, an NBA great who won 11 titles with the Boston Celtics and was the first Black head coach in the league, passed away "peacefully" on Sunday, according to a statement sent by his family on his verified Twitter account. Russell won all 11 of his titles with the Celtics. Russell's cause of death was not disclosed. He was 88.

"It is with a very heavy heart we would like to pass along to all of Bill's friends, fans, & followers," the statement reads. "Bill Russell, the most prolific winner in American sports history, passed away peacefully today at age 88, with his wife, Jeannine, by his side. Arrangements for his memorial service will be announced soon.

"Bill's two state championships in high school offered a glimmer of the incomparable run of pure team accomplishment to come: twice an NCAA champion; captain of a gold-medal-winning US Olympic team; 11 times an NBA champion; and at the helm for two NBA championships as the first black head coach of any North American professional sports team.

"Along the way, Bill earned a string of individual awards that stands unprecedented as it went unmentioned by him. In 2009, the award for the NBA Finals most valuable player was renamed after two- time Hall of Famer as the 'Bill Russell NBA Finals Most Valuable Player Award.'

"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. 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."

Besides redefining the game of basketball, the Boston Celtics player also re-defined the position of the Black athlete activist.

“Bill Russell was the greatest champion in all of team sports," NBA commissioner Adam Silver said in a statement, according to USA Today. "The countless accolades that he earned for his storied career with the Boston Celtics – including a record 11 championships and five MVP awards – only begin to tell the story of Bill’s immense impact on our league and broader society. Bill was the ultimate winner and consummate teammate, and his influence on the NBA will be felt forever."