“Given the sort of business we are in,” he later remarked, “usually when you get a call that early in the morning, it is something disastrous”, but it was “a wonderful way to wake up”.

There was no doubt the Nobel committee recognised the work of the thousands of unsung UN staff Annan led, striving anonymously behind the headlines – bearing the brunt of the outflow of Afghan refugees, waging the long and thankless battle to overcome poverty in Africa, fighting the scourge of HIV/Aids and other killer diseases, and patrolling the front lines in 16 peacekeeping operations around the world.

But it was also a tribute to the way the UN, under this remarkable leader, had become the one indispensable global organisation in our globalising world.

The man who brought the UN to the point of being worthy of the Nobel was unusual, first of all, for being the first to climb the ranks of the organisation from its lowest professional level to the very top. When Kofi Annan became Secretary-General at the beginning of 1997, he had not been a global figure like some previous contenders for the post; those who made it their business to follow the UN knew his résumé, but not his biography.

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Of his popularity with the staff there was no doubt: the jubilation in the corridors and offices of the UN Secretariat when the news of his election was first announced had to be seen to be believed.

For UN officials beleaguered by ill-informed criticism and beset by financial crises, anxious about the polemics surrounding the defenestration of the previous Secretary-General and crushed by the rapidity with which the post-cold war euphoria about a “new world order” had soured, the ascent of a man who knew their problems and their strengths was a shot in the arm.

But it was not the fact that he was an insider, nor even that he had worked for the UN in headquarters and the field across a remarkable range of areas – budget, personnel, refugees, and peacekeeping – that explained the continued exhilaration at the UN when he was re-elected to a second term in 2001, or the weeping, cheering throng that greeted him as he entered the Secretariat building after learning of his Nobel win.

It was something altogether simpler. Kofi Annan possessed that rare ingredient not always found in successful men: he was a wonderful human being.

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Born into a family of traditional chiefs of the Fante tribe in Ghana, Kofi Annan became a student leader of note in the country. A scholarship brought him to college in the United States (and later in Geneva) and, unusually for a bureaucrat, he took a degree in management from the Massachusetts Institute of Technology. More important, for those of us who worked with him, he had an unrecognised PhD in people.

He took the trouble to relate to others – young or old, senior or junior, ambassador or security guard. He listened patiently; he always made the time for an inquiry about your family or some trifling personal circumstance in your life. Time after time I saw visitors leave his presence overwhelmed by his warmth.

As a result, his personal qualities were widely seen as the key to his professional success. His family saw his humanity first. I will never forget the time when, as a single parent, he went to his seven-year-old son’s school’s Mothers’ Day celebration because his son wailed: “But all the other mothers will be there!”

UN officials knew him as a boss who extended trust and loyalty, who stood up for his staff, gave them credit for their accomplishments and took full responsibility for their mistakes.

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Annan was a man of rare wisdom, one whose advice and judgment was always respected by his peers as well as his subordinates. He had a gift for management that went well beyond anything that could be learned at business school; he picked his collaborators well and got the best out of them, unfailingly helping people fulfil a potential they might not even have realised they possessed.

He was a man of principle who did not hesitate to express his convictions; his tenure in office was marked by his firm determination to “put the individual human being at the centre of everything the UN does” and his willingness to challenge the dogma of sovereignty when it was used as a shield for abuses by governments.

Above all, he had an extraordinary inner calm: no one ever saw him angry, depressed, excited or in a panic. Even the UN’s most trenchant critics saw him as a man of integrity, humanity and deep personal strength. Like a yogi, he could walk on a different plane, with a strong, still centre to him in which he was deeply anchored.

A record-breaking sprinter in his youth – his collegiate mark in the 60-yard dash stood for decades – Kofi Annan revealed the tirelessness, stamina and patience of a long-distance runner, even after ceasing to be Secretary-General.

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He was roped in to deal with global crises in Ghana, Syria and Myanmar. Throughout the ups and downs of the UN’s efforts to cope with the new world disorder in recent years, he stayed strong, serene and focused.

And he never lost his modesty, or his sense of humour. A few years ago he told me about the time, very soon after he had relinquished his highly successful 10-year tenure the organisation’s leader, when he was walking with some friends and a couple of security guards down a street in Rome and a woman rushed up to him.

She was beside herself: “I can’t believe it! I can’t believe it!” she kept saying, jumping up and down in joy. “It’s actually you! Here in Rome! And I can shake your hand!” She did, vigorously, and then asked for an autograph. Annan had just begun signing when she went on, “I’d love to see my friends’ faces when I tell them I have actually met Morgan Freeman!”

“So what did you do?” I asked Annan. “How mortifying!”

The world’s former top diplomat smiled. “I had already begun signing my name,” he said, “so after writing ‘Kofi’, which I couldn’t change, instead of adding ‘Annan’, I signed ‘Freeman’.”

“After all,” he mused, “I am now a free man!”

He is a free man today, free of the world, but to each of us who was touched by him, his life and legacy will stay with us forever.

A former UN Under-Secretary-General under Kofi Annan, Shashi Tharoor is currently a Member of Parliament in India