I really hate to be the dick in this situation, but it's muhammad ali. I thought it might be good to at least spell the man's name right. The comparison as far as careers is not really there. Ali had rivals like Frazier and Norton that beat him 1/3 times. Fedor never really had a rival. Also Ali's career is different in that his prime was taken away from him. Is there any doubt that losing three years in his prime hurt him? Fedor never lost that time. I do think the comparison as one of the greats of the era that had some losses at the end of their career is apt.
As far as a public figure, there is no comparison. While Ali was very polarizing during his career, he was symbol to a lot of people, especially African Americans. He stood up to the system and at his own peril. What has made Ali more well loved in later years is that he was made right for what he stood up for. Obviously the equal rights for all citizens is something that is for the most part believed in within the US. Also it is a consensus for most historians that the Vietnam War was a mistake and not necessary. What Ali did for the people of this country transcends sport. He, whether he meant to or not, was a civil rights and peace advocate during one of the most inwardly tumultuous times of our country's history in the last century.