If you mean boxer Cassius Clay, his various name changes had nothing to do with having a dislike (or otherwise) of fighting.
In 1964, four years after his first professional fight, Cassius Marcellus Clay Jr. defeated Sonny Liston to become heavyweight champion of the world, after which he revealed that he was a member of the Nation of Islam. He changed his name to Cassius X, discarding his surname as a symbol of his ancestors' enslavement, as had been done by other Nation members such as Malcolm X.
Not long afterwards he was given the name Muhammad Ali by the leader of the Nation, Elijah Muhammad, who revealed the name to Ali as "his true name".
Although refusing to join the US Army in 1966 as a conscientious objector, Muhammad Ali continued to box whilst banned from doing so professionally in the US. The ban was lifted in 1970.
He converted from the Nation of Islam to orthodox Sunni Islam in 1975, and continued boxing for six more years until his retirement in December 1981.