The most successful athlete in American sports history has passed away.
Boston Celtics legend Bill Russell died "peacefully" Sunday at age 88, according to a statement shared on his official Twitter account.
"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.
Russell is widely considered one of the greatest NBA players of all time, and his 11 championships in 13 seasons with the Celtics are tied with the Montreal Canadiens' Henri Richard for the most titles of any player in a North American professional team spot.
In addition to his 11 titles, 12 All-Star appearances and five NBA MVP awards, Russell also won two championships as a player/coach in 1968 and 1969, a pair of NCAA titles with the San Francisco Dons in 1955 and 1956 and an Olympic gold medal in 1956.
Russell was much more than a basketball player, however. He emerged as a leader in the American Civil Rights movement during the 1960s, participating in the 1963 March on Washington to advocate for civil rights and supporting boxer Muhammad Ali after his decision not to participate in the Vietnam War.
Russell was awarded the Presidential Medal of Freedom in 2011.
"Bill stood for something much bigger than sports: the values of equality, respect and inclusion that he stamped into the DNA of our league," NBA commissioner Adam Silver said in a statement Sunday. "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.
"Through the taunts, threats and unthinkable adversity, Bill rose above it all and remained true to his belief that everyone deserves to be treated with dignity."
Russell was enshrined to the Basketball Hall of Fame twice as both a player and a coach, a testament to his towering legacy as one of the sport's all-time greats.