In this May 25, 1965 file photo, Heavyweight champion Muhammad Ali stands over fallen challenger Sonny Liston, shouting and gesturing shortly after dropping Liston with a short hard right to the jaw in Lewiston, Maine. (AP Photo/John Rooney)
In this March 8, 1971 file photo, boxer Joe Frazier lands a left to the jaw of Muhammad Ali during their title bout at New York's Madison Square Garden. Frazier won on a unanimous decision and retained his heavyweight title. (AP Photo)
In this March 8, 1971 file photo, Joe Frazier, left, faces off against Muhammad Ali, right, on the ropes during the fourth round of their heavyweight title bout in New York. (AP Photo)
In this Feb. 26, 1964 file photo, Muhammad Ali (Cassius Clay) uses a variety of bobbing and weaving to stay clear of the left arm of Sonny Liston in their title fight in Miami Beach, (AP Photo)
This is a Oct. 30, 1974 file photo Muhammad Ali watches George Foreman head for the canvas after being knocked out in the eighth round of their match in Kinshasa, Zaire. (AP Photo, File)
In this Oct. 1, 1975 file photo, Heavyweight champion Muhammad Ali connects with a right against challenger Joe Frazier in the ninth round of their title fight in Manila, Philippines. Ali won the fight on a decision to retain the title. (AP Photo/Mitsunori Chigita)
In this Sept. 28, 1976, file photo, challenger Ken Norton, left, and heavyweight champion Muhammad Ali trade right punches in the late rounds of their title fight in New York's Yankee Stadium. (AP Photo/File)
In this Oct. 1, 1975, file photo, Muhammad Ali, left, grimaces as he exchanges blows with Joe Frazier in the first round of their title bout at the Coliseum in Manila, Philippines. It was, Muhammad Ali would later say, the closest thing to death he had ever known.(AP Photo/Mitsunori Chigita, File)
In this Oct. 2, 1980 file photo, World heavyweight champion Larry Holmes, left, pounds challenger Muhammad Ali in the corner during championship fight in Las Vegas, Nev., . Holmes won when Ali failed to answer the bell to start the 11th round. (AP Photo, File)