Who is Cassius Clay, and what is he known for in One Crazy Summer?

Cassius Marcellus Clay Jr. was the original name of the famous boxer Muhammad Ali, who later became the World Heavyweight Champion. Clay’s father was named after a well-known nineteenth-century abolitionist, but Ali associated the name with slavery. In One Crazy Summer, the girls see posters of Ali at the People’s Center. The book takes places in 1968. Ali had changed his name in 1961 after converting to Islam. He first won the title of Heavyweight Champion in 1964 by defeating reigning champion Sonny Liston. He held onto this title by beating a total of 21 boxers. In 1966, when he was drafted, he refused induction into the US Army as a conscientious objector, citing his opposition to war because of the Qu’ran’s teaching and especially to the Vietnam War because he saw no need to fight the Vietnamese people. For taking this position, he was convicted of draft evasion and temporarily banned from professional boxing, but the Supreme Court overturned his conviction in 1971 so he was able to resume competing.
https://www.britannica.com/biography/Muhammad-Ali-boxer