Prison began his transformation from reluctant terrorist to conscience of a nation to a living martyr whose unbending fortitude and moral authority were admired around the globe.
It is what he did after prison, after becoming the first black president of South Africa in its first democratic election, that elevated him to supreme moral status. Choosing to serve only one term when he easily could have become president for life, as other Lilliputian African leaders have done, he instead helped draft a strong constitution that protected the rights of all, even the whites who had denied him his.
The onetime cattle herder became a beacon of light, one of the few political leaders equal to our iconic George Washington and Abraham Lincoln, enormous figures in history. Like Washington and Lincoln (who were military victors in war), after his triumph in winning freedom for his people, Mandela chose cleansing forgiveness over bloody revenge.
Mandela's luminous greatness was in how he overcame his suffering and anger, and perhaps the hate that would have consumed any other mortal man. Instead, he projected dignity and calm that set an example for black South Africans, all of Africa and the world.
If I were in his position, would I have been so magnanimous as to set up a Truth and Reconciliation Commission, but not to prosecute and punish the evildoers? I hope so, but I don't think so.
None of this was easy, because his reconciliation had to mollify both fearful whites and angry blacks. An African nationalist and a socialist, he was also a realist. Looking at other post-colonial African nations, he knew that if whites fled they would take their money and know-how with them. That would be a catastrophe for the nation.
"Courageous people do not fear forgiving, for the sake of peace," he said.
Given the crimes, brutality and murder of the former Afrikaner regime, that was a remarkable choice, the hardest choice, but the right choice.
He also had a keen sense of public relations and drama. In 1995, South Africa hosted the Rugby World Cup and black South Africans had long hated the all-white Springboks. Mandela urged all South Africans to cheer their team and when the Springboks beat New Zealand for the championship, Mandela presented the trophy to Springboks' Afrikaner captain Francois Pienaar wearing a Springboks jersey with Pienaar's No. 6.
With that gesture, "Mandela won the hearts of millions of white rugby fans," de Klerk said later.
Mandela always liked sports, and during his earlier life he flirted with communism, which always talks a better game than it delivers, but its atheism was offensive to his deep Christian faith. Mandela also went back and forth between nonviolence and (necessary?) violence, at the end choosing conciliation.
I am not alone in falling short of Mandela's exemplary example. Look around Africa (and the Middle East) and cry for the lack of leadership, the absence of men with the greatness of Washington and Lincoln and Gandhi and Mandela, the magnificent healers.
While South Africa is far from perfect - it has an alarmingly high crime rate, and government corruption even under Mandela was epidemic - it is not torn by civil war nor plundered by rapacious tyrants. South Africa's rocky democracy is still in better shape than almost anywhere else in Africa.
History may remember him first as a freedom fighter, and that he was. I hope history pays even more attention to his role as conciliator and herder of personal forgiveness because that is what saved South Africa from civil war and chaos.
He was a man you see once in a lifetime. Now he belongs to history - not black history, not African history, but human history.
On Twitter: @StuBykofsky