Ali once calculated that he had taken 29,000 punches to the head and made $57 million in his pro career, but the effect of the punches lingered long after most of the money was gone. That didn't stop him from traveling tirelessly to promote Islam, meet world leaders and champion legislation dubbed the Muhammad Ali Boxing Reform Act.

Although slowed in recent years, he managed to make numerous appearances, including a trip to the 2012 London Olympics. Despised by some for his outspoken beliefs and refusal to serve in the U.S. Army in the 1960s, an aging Ali became a poignant figure whose mere presence at a sporting event would draw longstanding ovations. With his hands trembling so uncontrollably that the world held its breath, he lit the Olympic torch for the 1996 Atlanta Games in a performance as riveting as some of his fights.