As secretary general of the UN, he dared to ruffle feathers as he defended the body and its work.

Kofi Annan’s decade-long tenure as UN secretary general was memorable for the multiple international crises on his watch and the extraordinary calm he exuded while trying to deal with their consequences – both for the world and a body that rarely managed to perform as well as its founding fathers had intended.

Like previous and subsequent UN chiefs, the mild-mannered Ghanaian quickly discovered that the tasks he had to carry out felt simultaneously unachievable and thankless because of the constant squabbling and conflicting interests of member states, especially the five veto-wielding permanent members of the security council.

The September 11 attacks and the 2003 invasion of Iraq left an especially indelible imprint. It was all the more remarkable, then, that when he left office in 2006 he was showered with plaudits – repeated on the news of his death – about his performance on the 38th floor of UN HQ on New York’s East River from 1997 to 2006.

Annan was no stranger to controversy before succeeding Egypt’s Boutrous Boutrous-Ghali in 1997. He had headed the UN’s peacekeeping department when the Rwandan genocide of 1994 was the worst such episode since the Holocaust.

But when he visited the country a few years later he had the guts to remind people that for all the shortcomings of the body he represented, it was Rwandans themselves who had carried out terrible atrocities.

No one questioned his commitment to promoting justice, universal human rights, peace and development – to make the world a better place and not to surrender to cynicism. Idealism, however, was not enough and Annan combined the qualities of an accomplished diplomat and experienced administrator of a notoriously labyrinthine bureaucracy.

Above all he understood, unlike others at the UN, that there was no point in grandstanding unless the US was on side; that was especially relevant during the Kosovo crisis of 1999. Annan’s sense of realpolitik about how the world works was perhaps his greatest asset.

Spats and tensions were inevitable. In 1998 he ruffled feathers in Washington and beyond – in Bill Clinton’s second term – when he said that Saddam Hussein was someone he could “do business with”. In the wake of the war, the UN suffered terrible blows, not least when its Baghdad HQ was targeted by a suicide bomber.

For anyone covering international affairs and diplomacy in those turbulent years, Annan was a towering figure but one whose personal style and exquisite manners created an impression of a man who was genuinely committed to civilised dialogue.

Annan was kind, thoughtful and invariably smiling. On a trip to Africa, he candidly advised the BBC’s UN correspondent Rob Watson on his mantra for surviving arduous journeys: “Eat when you can, drink when you can, sleep when you can and go to the can when you can.”

In recent years his most high-profile role was thrust upon him in 2012, when he was appointed the UN-Arab League joint special envoy for Syria as the protests of the Arab spring were morphing fatefully into the bloodiest war of the 21st century.

Annan was characteristically careful and modest – and also honest enough to admit failure after a bleak six months. But he justly condemned the “destructive competition” of the world’s most powerful states and their betrayal of the values embodied by the UN.