He was a fidgeter. Whether it was the pen on his desk, or the cutlery on his table, they were rarely left still for long. Never walking, except at speed, or listening to a briefing without his eyes signalling an eagerness to hear the next point so he could act on it, Kofi Annan was a man in a hurry.

Invariably described as calm, quiet and patrician, Annan was in truth a restless revolutionary – impatient with the state of the world, unwilling to accept the status quo, and infused with a life-long belief that peaceful change was possible. As the first Secretary-General appointed from within the ranks of the United Nations, Annan immediately seized the opportunity of low expectations on the part of global leaders used to the imperious ways of his predecessor.

Travelling with him in his first year of office as Secretary-General on missions designed to introduce him to presidents and prime ministers, I witnessed time and again a remarkable exchange. His hosts would begin with a sceptical look of having to adjust to a career official as UN Secretary-General, and then, over the course of an hour devoted to setting out Annan’s agenda of a revitalised UN, would conclude by asking, insistently, how they could help make his mission a success.

Annan knew better than anyone that a UN Secretary-General only had the power of persuasion – and with a mix of moral urgency and hard-won pragmatism proceeded to convert one global leader after another to his cause. From his very first day as Secretary-General, he sought to build out of the ashes of the tragedies of Bosnia and Rwanda a new compact between the United Nations and the “We, the Peoples” in whose name its charter was written.

The failures of the international community in Bosnia and Rwanda had many fathers. And he knew that as head of the UN Peacekeeping Department he was one of them. On Bosnia, he came to recognize that the UN for too long allowed the principle of neutrality to morph into complicity with Serbian aggression; on Rwanda, he lived with the knowledge of having rejected a call from the UN Force Commander on the ground to seize a weapons cache in the days before the genocide. He knew that there was no certainty that such a mission would have succeeded – but he also recognized that there was no certainty it couldn’t have derailed the murderous plans of the Hutus. That he received only rejection to his desperate pleas for troops from dozens of governments after the genocide had started, when no one could doubt its magnitude, did not diminish his own burden of responsibility.

His response, once elected Secretary-General, however, was deeply subversive.  He first commissioned two independent reports on Bosnia and Rwanda – both of whose critical conclusions he acknowledged and accepted publicly; then, he set out over the course of a number of speeches and statements to develop a new norm of humanitarian intervention premised on the principle that national boundaries no longer could be used as a shield for gross and systematic violations of human rights.

It is difficult now – in these very different times – to recognize just how radical an act this was. For an African. For a life-long official of an organization created out of the end of colonialism and dedicated to non-interference in internal affairs of newly liberated countries. For a peacemaker too scarred by conflict not to recognize the temptation this doctrine would present to those who would use it to wage war in the name of peace. And yet he persisted, because ultimately it was the cause of the individual man, woman and child in peril – rather than the member states and leaders so often responsible for their suffering – that was his animating mission as Secretary-General. In this act, he reset the moral compass of the United Nations.

At ease with the world and his own place in it – and of a time and a class when courtesy, manners and an easy laugh were the natural expressions of a generous soul – Annan never responded in kind to the sometimes low attacks on his leadership. Nor was he unaware of the myriad ways in which the UN – and he as its leader – fell short of the expectations of the peoples of a world too often promised too much by members of an international community still bound by doctrines of narrow self-interest. His own deepest sense of personal loss grew out of the ruinous Iraq war he did so much to prevent when some of his closest colleagues and friends – including Sergio Vieira de Mello, Nadia Younes and Rick Hooper – were killed in the bombing of the Baghdad UN headquarters fifteen years ago last week.

In his speech accepting the Nobel Peace Prize in 2001, Annan drew a direct line between the single life and the fate of the world: “A genocide begins with the killing of one man – not for what he has done, but because of who he is. A campaign of ‘ethnic cleansing’ begins with one neighbour turning on another. Poverty begins when even one child is denied his or her fundamental right to education. What begins with the failure to uphold the dignity of one life, all too often ends with a calamity for entire nations.”

For Sergio, Nadia, Rick and the thousands of others who dedicated their careers to serving the UN in some of the world’s most difficult war zones, Annan’s words and example served as enduring sources of solidarity and inspiration. They knew Annan was one of them, and that he was imbuing their sacrifice with a greater purpose and honour that only could come from a devotion to the cause of ending the suffering of individual men, women and children.

Devoted till the very end of his life to the cause of democratic change on his beloved Continent of Africa, he went to Zimbabwe only last month to urge its new leaders to mark the end to the Mugabe dictatorship with a commitment to building a legitimate and accountable government. Perhaps this last mission will bend one more decision, one more judgement, in favour of justice, development and peace in Africa – and for that, he would have been grateful.

Nader Mousavizadeh, Co-Founder and Co-CEO of Macro Advisory Partners, served as an aide to UN Secretary-General Kofi Annan from 1997-2003 and is the co-author, with Annan, of “Interventions: A Life in War and Peace.”