Rich O'Brien's Top 10 Heavyweights

He said he was "The Greatest" and, you know what? He was. Speed, grace, a transcendent ring intelligence and miraculous resilience made Ali a legend in the ring.

The Brown Bomber was was the classic boxer-puncher and the greatest finisher in heavyweight history.

At his peak, Liston was an absolute destroyer (ask Floyd Patterson) and a far more complete fighter than he is given credit for.

His 20 successful title defenses are second only to Louis' 25. With an unmatched jab and tremendous ring smarts, Holmes described his crafty style by saying, "You always got to make somebody drunk before you mug him."

The first black heavyweight champion and the first truly modern champion, Johnson had great speed, power in both hands and was a defensive wizard.

The "Manassa Mauler" was a ferocious attacking force and pound-for-pound the hardest puncher in heavyweight history. Electrifying in action.

Though inelegant at times, Big George was an irresistible offensive force. In 1987, after a 10-year layoff, he returned older and heavier but smarter than ever and nearly as effective.

Relentless, swarming and implacable, with that terrible, swift left hook, there was nowhere to hide when Joe was Smokin.

The only heavyweight champion to retire undefeated, Marciano was a bruising puncher seemingly impervious to pain. Often outsized, the Brockton Blockbuster was never outworked.

The youngest heavyweight champion in history, Iron Mike in his prime was a positively pyrotechnic blend of speed and power -- and one of boxing's most intimidating figures.