Boxing legend Muhammad Ali who was admitted on Monday to a Phoenix-area hospital with a respiratory ailment died Friday night of septic shock due to unspecified natural causes. Ali was born Cassius Marcellus Clay Jr in Louisville, in western Kentucky, on January 17, 1942, and was known as the "Louisville Lip" early in his boxing career because of his playfully boastful nature. He began training when he was 12 years old and at 22, he won the world heavyweight championship from Sonny Liston in 1964.  Shortly after that, Clay converted to Islam, changed his "slave" name to Ali. He was stripped of his world boxing crown for refusing to join the U.S. Army and fight in Vietnam, Ali returned in triumph by recapturing the title and starring in some of the sport's most unforgettable bouts. In his prime as a fighter, Ali spoke out against racism, war and religious intolerance, while projecting a brash confidence and sense of pride that became a model for African-Americans during 1960's and 1970's. At the time of his death, he was 74 years.