Muhammad Ali made 9 successful title defenses during his first heavyweight championship reign, from 1964 to 1967.
Ali won the championship by defeating Sonny Liston on February 25, 1964. He defended the title against Liston in their rematch, then retained it against Floyd Patterson, George Chuvalo, Henry Cooper, Brian London, Karl Mildenberger, Cleveland Williams, Ernie Terrell and Zora Folley.
His reign ended in 1967 when the boxing authorities stripped him of the title after he refused induction into the U.S. Army during the Vietnam War. That administrative loss was not a defeat in the ring. The nine-defense figure refers specifically to this first reign, not Ali’s total number of defenses across all three championship periods.