Conversation so far:
When was Muhammad Ali born?
Cassius Marcellus Clay Jr. was born on January 17, 1942
Where was Muhammad Ali born?
Cassius Marcellus Clay Jr. was born on January 17, 1942 in Louisville, Kentucky
Who were Muhammad Ali's parents?
Muhammad Ali's father was a sign and billboard painter, and his mother, Odessa O'Grady Clay, was a domestic helper.
Did Muhammad Ali know his mother?
Although Cassius Sr. was a Methodist, he allowed Odessa to bring up both Muhammad Ali and his younger brother, Rudolph Rudy Clay
When did Muhammad Ali start boxing?
Muhammad Ali was first directed toward boxing by Louisville police officer and boxing coach Joe E. Martin.
Did Muhammad Ali win his first fight?
Muhammad Ali made his amateur boxing debut in 1954 against local amateur boxer Ronnie O'Keefe. He won by split decision.
Where did Muhammad Ali train?
For the last four years of Muhammad Ali's amateur career he was trained by boxing cutman Chuck Bodak.
How many fights did Muhammad Ali have?

Question: who was his biggest fight against
Self-contained rewrite: Who was Muhammad Ali's biggest fight against?