When police shot 60 black protestors dead in the Sharpeville massacre, the ANC radicalized and Mandela formed the military wing and became its first commander in 1961.
By 1962, he was imprisoned for inciting a strike and sentenced in 1964 to life in prison.
George Bizos, his friend of more than half a century, said that Mandela's "noble birth" had shaped his respect for others, even his foes.
When Bizos, who is white, first visited Mandela on Robben Island prison a month after his conviction in 1964, no fewer than eight white guards surrounded the prisoner on all sides. After enthusiastically embracing his friend, Mandela politely turned to his captors.
"This place has made me forget my manners, not introducing you to my guards of honor," Mandela told Bizos. "He introduced each one of them by their first and second name. They were really numbed by his behavior, and a white man embracing a black man."
He was "never aloof," Bizos told ABCNews.com in 2010.
But the man behind the prison-bound martyr was as complicated as he was celebrated.
"Sometimes I feel like the one who is on the sidelines who has missed life itself," he wrote in one of his letters, chronicled in the Anthony Sampson biography, "Mandela."
Mandela's release from prison at the age of 76 led to negotiations that ended decades of racist white rule and set the stage for his presidency in South Africa's first democratic elections in 1994.
He served one term and then retired from political life in 1999, establishing the Nelson Mandela Foundation to fight poverty, AIDS and illiteracy in Africa. Since then, his life story has been a beacon to the world.
But Mandela's personal life was fraught with operatic tragedy.
When then-president de Klerk released him from Victor Verster prison Feb. 11, 1990, Mandela learned that his wife of 30 years had been unfaithful.
His oldest and favorite son, Thembi, never once visited him in prison, and Mandela only learned about his death in a car accident by telegram in 1969.
He married his first wife, Evelyn Mase, in 1944, but they divorced after arguments over his political involvement. They had four children, a daughter who died in infancy and two sons who perished in adulthood. Mase died in 2005.
But it was his second wife, Winnie Madikizela-Mandela, who caused him crushing humiliation, taking a lover to her home while he was confined to prison.
"It was real agony for him, genuinely horrible," James Sanders, researcher for the biography, "Mandela," said. "She was a big superstar and she had a lover in her house."
Their long, passionate romance began in 1957. She was a social worker and 16 years younger than the 38-year-old activist. Marrying a year later, the couple radiated both political and sexual energy. They had two girls.
Madikizela-Mandela was never allowed to assume the role of first lady because of her infidelities.
Still active in South African politics, she is held in both awe as the "Mother of the Nation" and contempt, for her alleged involvement in human rights abuses, including the torture and murder of 14-year-old activist Stompie Moeketsi in 1989.
Just this month, South African prosecutors said they are considering charges against her, which she denied, following the exhumation of bodies believed to belong to two young activists last seen at her home 24 years ago.
But Mandela loved again, capping his 80th birthday in 1998 with his marriage to Graca Machel, the 52-year-old widow of Mozambican president Samora Machel, who died in a 1986 plane crash.
"Late in my life, I am blooming like a flower because of the love and support she has given me," Mandela said of the child rights activist, whom he met shortly after he was released from prison.
"If I could say in a very modest way that's what I was able to give him back," Machel, a noted campaigner for children's rights, said in a 1998 interview. "I'm happy that in his sunset years I was able to be there for him. And he is there for me."