Yet when Nelson Mandela was asked how his 27 years in prison, most of them on Robben Island, had affected him, his answer was unexpected. "I came out mature," he said.
Mr Mandela disappeared from the world with the reputation of a charismatic but often boastful lawyer, a keen boxer and ladies' man who did not have the temperament to remain undetected for long when he went underground. He returned a dignified old man who had won the respect of his captors, so much so that they were anxious to negotiate the handover of power to him. Thanks to Mr Mandela's imprisonment there, Robben Island is now a world heritage site, but when visitors see the conditions in which he was held, few find it easy to imagine how he retained his sanity, let alone triumphed over his oppression.
"Journeying to Robben Island was like going to another country," Mr Mandela wrote in his autobiography, 'Long Walk to Freedom'. "Its isolation made it not simply another prison, but a world of its own." He first saw it in May 1963, having been sentenced the previous October to five years for sabotage.
After another trial in Pretoria, this time for treason, he returned to the island in June 1964 and remained there until March 1982, when he was moved to the mainland. He did not walk to freedom until February 1990.
Mr Mandela recalls his first arrival on the island in his book: "We were met by a group of burly white warders shouting (in Afrikaans): 'Dis die Eiland! Hier gaan julle vrek!' (This is the Island! Here you will die!)" Immediately he showed the spirit of resistance that helped to carry him through, telling his fellow inmates to walk when the warders were shouting at them to run, and threatening legal action against one notoriously brutal figure who seemed about to hit him.
While Mr Mandela was never assaulted during his prison term, everything about the regime was designed to punish and humiliate black leaders who had had the temerity to demand equality with whites.
Category D political prisoners like him were allowed one 30-minute visit and one letter every six months. Anything deemed "political" in the letters would be cut out, so that often the prisoner received nothing but a tattered, indecipherable remnant of paper.
Even among inmates there was racial discrimination -- Mr Mandela recalled that he and other African prisoners were given shorts to wear, while Ahmed Kathrada, the only Asian among the group of African National Congress leaders who arrived on the island together, received long trousers. Africans also had a worse diet than Asian or mixed-race inmates. Removing these inequalities was among the first of many issues on which Mr Mandela and his fellow political prisoners mounted campaigns of passive resistance during their years on Robben Island.
Despite poor food, inadequate clothing in the wet and windswept Cape winter, and heavy labour in the island's lime quarry, where Mr Mandela's sight was damaged by the blinding glare of the sun on the quarry's blanched walls, he remained unbroken. "The challenge for every prisoner, particularly every political prisoner," he wrote, "is how to survive prison intact, how to emerge from prison undiminished, how to conserve and even replenish one's beliefs. . . The authorities' greatest mistake was to keep us together, for together our determination was reinforced. We supported each other and gained strength from each other."
The bullying, poorly-educated white warders were uncertain how to deal with these articulate, determined political prisoners, who seemed confident that they would one day prevail, no matter how long their sentences or how complete the white regime's apparent domination. By the early 1970s Mandela had tamed the prison authorities to the point where they would frequently consult him. Occasional attempts to revert to the old brutal regime were seen off, and concessions, such as the right to study, were won.
But Robben Island remained deeply isolated -- isolation worsened, Mr Mandela wrote, by the proximity of "the glass towers of Cape Town. The city looked agonisingly close, as though one could almost reach out and grasp it".
Above all, Nelson Mandela had to fill the endless years without ever knowing how long his imprisonment would last. He had been sentenced to life, and until the late 1980s apartheid's masters insisted that he would die behind bars.
"To survive in prison," he wrote, "one must develop ways to take satisfaction in one's daily life. One can feel fulfilled by washing one's clothes so that they are particularly clean, by sweeping a corridor so that it is free of dust, by organising one's cell to conserve as much space as possible.
"The same pride one takes in more consequential tasks outside prison, one can find in doing small things inside prison."
In March 1982, he was abruptly told that he was to be transferred to Pollsmoor prison on the mainland. The reason, it later emerged, was that the apartheid government thought he might prove more pliant in negotiations if he was kept apart from his comrades.
They soon discovered they were wrong, but for Mr Mandela, who had spent the best part of two decades on Robben Island, it was a wrench.
"A man can get used to anything, and I had grown used to Robben Island," he wrote.
"It had become a place where I felt comfortable." More than that: as he himself said, his ordeal there was the making of him. (© Independent News Service)