So when he criticises US foreign policy in terms every bit as harsh as those he used to condemn apartheid, you know something is up. In the past few weeks, he has issued a "strong condemnation" of the US's attitude towards Iraq, lambasted vice-president Dick Cheney for being a "dinosaur" and accused the US of being "a threat to world peace".
Coming from other quarters, such criticisms would have been dismissed by both the White House and Downing Street as the words of appeasement, anti-Americanism or leftwing extremism. But Mandela is not just anyone. Towering like a moral colossus over the late 20th century, his voice carries an ethical weight like no other. He rode to power on a global wave of goodwill, left office when his five years were up and settled down to a life of elder statesmanship. So the belligerent tone he has adopted of late suggests one of two things; either that some thing is very wrong with the world, or that something is very wrong with Mandela.
What Mandela believes is wrong with the world is not difficult to fathom. He is annoyed at how the US is exploiting its overwhelming military might. Earlier this month, after President Bush would not take his calls, he spoke to secretary of state Colin Powell and then the president's father, asking the latter to discourage his son from attacking Iraq.
"What right has Bush to say that Iraq's offer is not genuine?" he asked on Monday. "We must condemn that very strongly. No country, however strong, is entitled to comment adversely in the way the US has done. They think they're the only power in the world. They're not and they're following a dangerous policy. One country wants to bully the world."
Having supported the bombing of Afghanistan, he cannot be dismissed as a peacenik. But his assessment of the current phase of Bush's war on terror is as damning as anything coming out of the Arab world. "If you look at these matters, you will come to the conclusion that the attitude of the United States of America is a threat to world peace."
And then there is the dreaded "r" word. Accusations of discrimination do not fall often or easily from Mandela's lips, but when they do, the world is forced to sit up and listen. So far, he has fallen short of accusing the west of racism in its dealings with the developing world, but he has implied sympathy with those who do. "When there were white secretary generals, you didn't find this question of the US and Britain going out of the UN. But now that you've had black secretary generals, such as Boutros Boutros Ghali and Kofi Annan, they do not respect the UN. This is not my view, but that is what is being said by many people."
Most surprising in these broadsides has been his determination to point out particular individuals for blame. As a seasoned political hand, Mandela has previously eschewed personal invective but has clearly made an exception when it comes to Cheney. In 1986, Cheney voted against a resolution calling for his release because of his alleged support for "terrorism". Mandela insists that he is not motivated by pique. "Quite clearly we are dealing with an arch-conservative in Dick Cheney... my impression of the president is that this is a man with whom you can do business. But it is the men around him who are dinosaurs, who do not want him to belong to the modern age."
In fact, behind the scenes, the White House is attempting to portray Mandela, now 84, as something of a dinosaur himself - the former leader of an African country, embittered by the impotence that comes with retirement and old age. It is a charge they have found difficult to make stick. Mandela has never been particularly encumbered by delusions of grandeur. When asked whether he would be prepared to mediate in the current dispute, he replied. "If I am asked by credible organisations to mediate, I will consider that very seriously. But a situation of this nature does not need an individual, it needs an organisation like the UN to mediate. A man who has lost power and influence can never be a suitable mediator."
In truth, since leaving office he has shown consummate diplomatic skill. In 1999, he persuaded Libyan leader Colonel Gadafy to hand over the two alleged intelligence agents indicted in the 1988 Lockerbie bombing. He was touted as a possible mediator in the Middle East - a suggestion quashed by the Israeli government, which was apartheid's chief arms supplier.
Last year he was personally involved in the arrangement - sanctioned by the UN - to send South African troops to Burundi as a confidence-building measure in a bid to forestall a Rwandan-style genocide. That does not mean he always gets it right. He advocated a softly-softly diplomatic approach towards the Nigerian regime when Ken Saro-Wiwa was on death row. Saro-Wiwa was murdered and Abacha's regime remained intact. Nor does it mean that he is above criticism. Arguably, he could have done more to redistribute wealth during his term in office in South Africa, and he maintained strong diplomatic relations with some oppressive regimes, such as Indonesia. In July, a representative of those killed in the Lockerbie disaster described Mandela's call for the bomber to be transferred to a muslim country as "outrageous". But it does mean that he is above the disparagement and disdain usually shown to leaders of the developing world that the west find awkward.
But if there is something wrong with Mandela it is chiefly that for the past decade he has been thoroughly and wilfully misunderstood. He has been portrayed as a kindly old gent who only wanted black and white people to get on, rather than a determined political activist who wished to redress the power imbalance between the races under democratic rule. In the years following his release, the west wilfully mistook his push for peace and reconciliation not as the vital first steps to building a consensus that could in turn build a battered nation but as a desire to both forgive and forget.
When he displayed a lack of personal malice, they saw an abundance of political meekness. There is an implicit racism in this that goes beyond Mandela to the way in which the west would like black leaders to behave. After slavery and colonialism, comes the desire to draw a line under the past and a veil over its legacy. So long as they are preaching non-violence in the face of aggression, or racial unity where there has been division, then everyone is happy. But as soon as they step out of that comfort zone, the descent from saint to sinner is a rapid one. The price for a black leader's entry to the international statesman's hall of fame is not just the sum of their good works but either death or half of their adult life behind bars.
In order to be deserving of accolades, history must first be rewritten to deprive them of their militancy. Take Martin Luther King, canonised after his death by the liberal establishment but vilified in his last years for making a stand against America's role in Vietnam. One of his aides, Andrew Young, recalled: "This man who had been respected worldwide as a Nobel Prize winner suddenly applied his non-violence ethic and practice to the realm of foreign policy. And no, people said, it's all right for black people to be non-violent when they're dealing with white people, but white people don't need to be non-violent when they're dealing with brown people."
So it was for Mandela when he came to Britain in 1990, after telling reporters in Dublin that the British government should talk to the IRA, presaging developments that took place a few years later. The then leader of the Labour party, Neil Kinnock, called the remarks "extremely ill-advised"; Tory MP Teddy Taylor said the comments made it "difficult for anyone with sympathy for the ANC and Mandela to take him seriously."
He made similar waves in the US when he refused to condemn Yasser Arafat, Colonel Gadafy and Fidel Castro. Setting great stock by the loyalty shown to both him and his organisation during the dog days of apartheid, he has consistently maintained that he would stick by those who stuck by black South Africa. It was wrong, he told Americans, to suggest that "our enemies are your enemies... We are a liberation movement and they support our struggle to the hilt."
This, more than anything, provides the US and Britain with their biggest problem. They point to pictures of him embracing Gaddafi or transcripts of his support for Castro as evidence that his judgment has become flawed over the years. But what they regard as his weakness is in fact his strength. He may have forgiven, but he has not forgotten. His recent criticisms of America stretch back over 20 years to its "unqualified support of the Shah of Iran [which] lead directly to the Islamic revolution of 1979".
The trouble is not that, when it comes to his public pronouncements, Mandela is acting out of character. But that, when it comes to global opinion, the US and Britian are increasingly out of touch. Additional reporting by Shirley Brooks.