Nelson Mandela is not a saint, despite the efforts of his assorted minders, gatekeepers and hangers­on to regulate public access to him and polish his marble.

His autobiography, Long Walk to Freedom, makes it clear that he can be unreasonably stubborn (a quality he traces to his father) and imperious and that he is capable of towering rages when he believes his dignity and authority have been crossed.

Long Walk contains a remarkable description of his near-physical assault, and then verbal mauling, of a Robben Island prison chief who spoke slightingly of his wife, Winnie.

His reaction is telling: "Even though I had silenced [Lieutenant] Prins he had caused me to violate my self-control, and I considered that a defeat at the hands of my opponent."

A democratic traditionalist who often harks back to the consultative style of the Thembu regency of his childhood, his practice is to listen and weigh his moves carefully. But once he has made up his mind, it sets like metal.

Ironically, Winnie Madikizela-Mandela would herself fall victim to one of his coldly uncompromising furies when, as a deputy minister in his government, she travelled abroad in defiance of his wishes.

His former spokesperson, Parks Mankahlana, also told me he is keenly sensitive to media criticism. During his presidency he summoned black journalists to a meeting at the Union Buildings where he accused them of being the tools of their white editorial masters.

It is no less a mistake to cast him as a latter-day St Francis or paragon of Gandhian non-violence. From the early 1950s, when the ANC was formally committed to peaceful resistance to apartheid, he was gravitating towards a military solution. He and Walter Sisulu were dressed down by angry party leaders, including Albert Luthuli, for an unauthorised jaunt to China to discuss revolutionary war.

Yet Mandela is equally incapable of the vices of small men -- cruelty, vindictiveness, petty intrigue or deluded grandeur.

Long Walk is striking for its complete absence of boastfulness and its frequent wry put-downs of the author, particularly as a gauche rural youth. It describes, for example, his perspiring assault on a chicken wing with a knife and fork, which were new to him, under the mocking gaze of the local reverend's pretty daughters.

By common consent Mandela is a "great" man, perhaps the greatest of his era. But what does this mean?

It implies, in the first place, a massive, rooted self-confidence and unshakeable sense of himself which neither the long degradation of Robben Island nor presidential power and world adulation have fundamentally altered.

To meet him is to feel his personal authority. In the early 1990s I witnessed powerful company executives stumble sheepishly to their feet, like schoolboys confronted by the headmaster, when he loomed unannounced at their lunch table.

In contrast with his successor, President Thabo Mbeki, he is perfectly at ease with both crowds and kings.

His sheer physical presence contributes to the spell he casts. For an African from the south of the continent, he is very tall and, for his age, slim and powerfully built. There is a slight Khoi-San cast to his features, which heightens the sense that he is an all-embracing African figure.

His autobiography underscores what one could describe as his martial virtues: his daring, physical courage and extraordinary mental toughness.

Days before judgement and sentence in the Rivonia Trial, with the death penalty a distinct prospect, he calmly wrote (and passed) University of London law exams. Even before sentencing he, Walter Sisulu and Govan Mbeki had decided not to appeal, reasoning that this would undermine their use of the trial as a political showcase.

The tale of his prison years has been endlessly retold, but from the vantage-point of a less barbarous age it is worth touching on what he went through.

Arriving on the island at the age of 46, he spent 13 years swinging a pick in a lime quarry, half-blinded by the glare.

The aim was to break the morale of the political prisoners -- unlike the Indian inmates, Africans were initially compelled to wear short trousers and denied socks and underwear. Prisoners were required to stand in the presence of warders and told to call them baas.

Mandela's response was to treat each humiliation and act of administrative malice as a "site of struggle". The balance of power slowly tilted in his favour over his 27 years inside to the point where he was allowed to spend his days studying, arguing politics with his friends and gardening.

The idea of "greatness" has been closely associated in many societies with military prowess ­- Alexander, Julius Caesar and Shaka are called "great" on the strength of not much more than their bellicose empire-building.

But in the past century the rise of the labour movement and a world human rights culture, and the related fight against colonial bondage, have given rise to a new set of world-historical icons who have enlarged human freedom and redefined humanist ideals. With Simón Bolivar, Ho Chi Minh, Amilcar Cabral and Yasser Arafat, Mandela is one of them.

His lack of bitterness and readiness not just to forgive, but also to share a liberated South Africa with his former oppressors was the source of the now-vanished optimism of his presidential term.

He understood that apartheid could not be defeated by peaceful means, but is not a violent man. Holidaying in the Eastern Cape in 1955, he was mortified when he ran over a large snake. "I do not like killing any living thing, even those creatures that fill some people with dread," he wrote.

No Easy Walk is strewn with touching examples of his kindness and old-fashioned chivalry. It describes, for example, the embarrassment of a white secretary at his first legal firm when she was seen taking dictation from him. "She took a sixpence from her purse and said stiffly: 'Nelson, please go out and get some shampoo from the chemist.' I left the room and got her shampoo."

He returns again and again to the pain inflicted on his family by his activism and long jail term and his torment over the government's persecution of Winnie while he was powerless to support her.

Ordinary people respond not just to Mandela the leader and emancipator, but also to Mandela the suffering man. Few could be unmoved by his testimony, during his divorce proceedings, of his terrible loneliness when he moved from prison to a dying marriage.

He is, at heart, an optimist who finds it hard to give up on his frail fellow creatures.

One of the central passages of No Easy Walk concerns the brutal Colonel Piet Badenhorst, who, assuming command of the prison in 1971, began rolling back the small gains the prisoners had accumulated. One of his habits was to urinate next to them at the quarry while they were eating.

Yet when Badenhorst was transferred after a determined campaign by the inmates, he summoned Mandela and told him, as one human being to another: "I just want to wish you people good luck."

"It was a useful reminder that all men, even the most seemingly cold-blooded, have a core of decency," was Mandela's reading of the incident, "and that if their hearts are touched, they are capable of changing."