Youth reigns eternal, the younger version of anyone will beat the older version. But outside the ring, Ali became far more than a boxer, he is almost universally recognized and beloved, so depending on what you mean by "greater" your answer may vary. In a boxing match the youngster would solve the rope a dope, but on the world stage, almost no one reached the level Ali did.

Ali was greater overall but clay was greater physically faster better reflexes but even though Ali was older he was more experienced and could take a better punch also Ali was a bigger icon outside the ring he also accomplished more as Ali

Ali because he's smarter, tougher and had more ring savvy than Clay. Ali fought with and beat the best of what is considered the golden era in heavyweight history - Frazier, Foreman, Norton, Quarry, Young, Shavers.

Ali

What exactly are you asking? Muhammad Ali and Cassius Clay are the same person.

Clay was greater, he was undefeated and never lost a fight.