Muhammad Ali was born Cassius Marcellus Clay in Louisville, Kentucky, on 17 January 1942, the son of a sign painter. He was named after a prominent 19th Century abolitionist.
When he was 12, he reported his bicycle had been stolen and told a police officer he was going to "whip" the culprit.
The officer, Joe Martin, trained young fighters at a local gym and suggested the youngster learn to box before he challenged the thief.
Muhammad Ali, the former world heavyweight champion whose boxing feats, showmanship and political activism made him one of the best-known figures of the 20th century, died on Friday aged 74.
Ali, who had long suffered from Parkinson's syndrome which impaired his speech and made the once-graceful athlete almost a prisoner in his own body, died a day after he was admitted to a Phoenix-area hospital with a respiratory ailment.
His youthful proclamation of himself as "the greatest" rang true until the end for the millions of people worldwide, who admired him for his courage both inside and outside the ring.
"Muhammad Ali was one of the greatest human beings I have ever met," said George Foreman, who lost to Ali in Zaire in a classic 1974 bout known as the "Rumble in the Jungle."
"No doubt he was one of the best people to have lived in this day and age. To put him as a boxer is an injustice."