After winning the championship from Liston in 1964, Cassius Clay revealed that he was a member of the Nation of Islam (often called the Black Muslims at the time) and the Nation gave Clay the name Cassius X, discarding his surname as a symbol of his ancestors’ enslavement, as had been done by other Nation members.
On Friday, March 6, 1964, Malcolm X took Clay on a guided tour of the UN building (for a second time). Malcolm X announced that Clay would be granted his “X.” That same night, Elijah Muhammad recorded a statement over the phone to be played over the radio that Clay would be renamed Muhammad (one who is worthy of praise) Ali (fourth rightly guided caliph).
Only a few journalists (most notably Howard Cosell) accepted it at that time. Venerable boxing announcer Don Dunphy addressed the champion by his adopted name, as did British reporters. The adoption of this name symbolized his new identity as a member of the Nation of Islam.