David Remnick, renowned author of Lenin's Tomb, was drawn to Ali the man and what he stood for in his heyday. His book on Ali received good reviews.

As Cassius Clay rose to prominence as a fighter, it was clear that he was not cut from the same mold as most other black champions that he was compared against. According to Remnick, Floyd Patterson was the "Good Negro" while Sonny Liston, a former convict, was the "Bad Negro." Liston easily beat Patterson, and Clay was next for him. Remnick states that Ali knew that Liston was powerful, so Clay pretended to be a madman. Liston was intimidated by Clay's conduct outside the ring and flustered by his speed inside the ring. Remnick is certain that Liston cheated by putting a foreign substance on his gloves for his Clay fight. But Clay overcame him anyway and became heavyweight champion in 1964.

Immediately after becoming champion, Clay announced that he was a member of the Nation of Islam and he changed his name to Mohammad Ali. Ali had known that the fight with Liston would have been cancelled if the public had known about his religion and membership in the Nation of Islam. Remnick devotes a lot of his book to Ali's spirituality and his relationship with Malcolm X and Elijah Muhammad.

Another key part of the book concerns Ali's refusal to serve in the Vietnam War. Ali's stance cost him a great deal in lost prize money. Remnick says it cost him his title: "His title which he had coveted from the age of twelve."

King of the World by David Remnick is about the life of Muhammad Ali from the time he was a young boy to when he won the world heavyweight championship. Remnick discusses how Ali revolutionized sports. Besides being an athlete, Ali fought against racial injustice.

Cassius Clay, popularly known as Muhammad Ali, was born during an era when boxing was influenced by the mob. Clay was strong-willed and disagreed with racial stereotypes and the mob’s influence when it came to boxing. Many boxing enthusiasts looked at him as a rebel due to his strong political and religious views; He legally changed his name to Muhammad Ali when he converted to Islam. His rebellious nature and conscience cost him his heavyweight championship title and license to box when he refused to be inducted into the U.S. Army during the Vietnam War.

Remnick touches on Ali's early life in Kentucky and his first fights. He also concentrates on the fight between Muhammad Ali and Sonny Liston. The fight propelled Ali into stardom. Remncik mentions prominent people in the 1960s such as John F. Kennedy, as well as prominent events of the time. More than simply discussing Muhammad Ali’s career as a boxer, however, Remnick focuses on the battles that Ali fought outside the ring.