Nelson Mandela was a remarkable person for how he lead his country out of apartheid, peacefully despite huge personal sacrifice that would have turned a lesser leader to retaliate for past transgressions.
Yes, Martin Luther King was made of similar stuff and an agent for peace between the races.
Cassius Clay, followed his conscience(?) to not enter military service when drafted, unlike the vast majority of us who were called and did serve. I do not see him rising to the level of King or Mandela. EW IMO does not even deserve discussion.
Lets respect Mandela's memory. A truly great man who is no longer with us. There are other's from other countries with vaguely comparable histories still playing out, but now is not the time to make such a list.