Ban Ki-moon has taken the "most impossible job in the world", as Trygve Lie, the first Secretary-General of the United Nations, famously said to his successor, Dag Hammarskjöld.

Before dealing with the role of the Secretary-General, it may be appropriate to look even further back into the past and recall the role of the Secretary-General of the League of Nations. In accordance with Article 6 of the Covenant of the League, he was exclusively an administrator, and the Secretariat of the League was never intended to be one of its principal organs.

In the Charter of the United Nations, however, the Secretariat was among the principal organs, most certainly also to grant to the Secretary-General some political prerogatives. In accordance with Article 97 of the Charter, the Secretary-General is "the chief administrative officer of the Organization", but additionally Article 99 stipulates that he "may bring to the attention of the Security Council any matter which in his opinion may threaten the maintenance of international peace and security". As a result, the Secretary-General has on many occasions extended his good offices or acted as a mediator.

In the early days of the United Nations, an atmosphere of extreme enthusiasm prevailed. Delegates were convinced that they had adopted a system of collective security that would ban all wars forever. As members of the Secretariat, we felt like pioneers. That feeling was shared by the first Secretary-General, Trygve Lie of Norway, who served from 1 February 1946 to November 1952. He probably realized that by being the first, any of his decisions was likely to become a precedent. For example, by appointing a Soviet national to head the Department of Political and Security Council Affairs, he set a trend for decades to come.

Trygve Lie was replaced by Dag Hammarskjöld of Sweden, who was appointed in April 1953 as the second Secretary-General. By then, the international situation had begun to deteriorate. The euphoria of earlier days was replaced by an atmosphere of extreme tension, the cold war, that led to the polarization of the world-and therefore of the United Nations-into two camps, East and West. The Security Council was almost paralysed by the repeated vetoes cast by the Soviet Union, which was facing an overwhelming majority from the West. Since one member of the United Nations family, the Security Council, had become incapacitated, others came to the rescue. Indeed, all Member States had a vested interest in the Organization and none of them wanted it to fail. As a result, some of the topics that the Council was unable to deal with because of the East-West confrontation were transferred to the General Assembly through a procedure established by resolution 377 (V) of 3 November 1950, entitled "Uniting for peace".

For other questions, which could not be discussed openly in the General Assembly, Mr. Hammarskjöld extended his good offices and resorted to quiet diplomacy, a trend that was followed by all his successors. On several occasions, he used the podium of the Assembly to reply publicly to the attacks of Nikita Khrushchev, Head of the Government of the USSR, who had advocated the replacement of the Secretary-General by three persons: one from the East, one from the West and one from the South, the famous "troika". In 1959, I was transferred to the Office of the Secretary-General to deal with matters related to the General Assembly. I was then able to witness on many critical occasions the extraordinary energy of the Secretary-General, who used to work late into the night.

Dag Hammarskjöld's successor, U Thant of Burma (now Myanmar), was well known to the New York diplomatic community, when in November 1961 he was appointed Acting Secretary-General, and in November 1962 Secretary-General to replace Dag Hammarskjöld who had perished with 15 of his collaborators in a plane crash on a mission of peace to Africa. Before his appointment as the third Secretary-General, U Thant had been Permanent Representative to the United Nations. I was quite familiar with his thinking, since I was working in his office, and on account of my knowledge of French he had asked me to be his private interpreter.

U Thant was a humble man, but he had very firm convictions. He promoted both in the General Assembly and during his missions abroad his motto of the "three Ds": decolonization, disarmament and development. He firmly believed in quiet diplomacy. Since I attended many of his private meetings, I can say with assurance that on many occasions during the difficult period of the cold war, he extended his good offices to act as a discreet mediator. He served as Secretary-General until 1971.

U Thant was followed by Kurt Waldheim of Austria, who served two full terms, from 1972 to 1981. Prior to his appointment as the fourth Secretary-General, he had held a number of diplomatic functions, including of Permanent Representative to the United Nations and Minister for Foreign Affairs. Throughout his mandate, especially during the first three years, Mr. Waldheim made it a practice to visit areas of special concern to the United Nations. As international relations were still hampered by the cold war, and the Security Council could not function properly, he often served as a mediator.

The fifth Secretary-General, Javier Pérez de Cuéllar of Peru, held that position from 1982 to 1991. His appointment came to him as a complete surprise, as he was just beginning to enjoy retirement in his country when he heard the news. He knew the United Nations inside out, since earlier in his career he had been Permanent Representative to the United Nations and later Under-Secretary-General for Special Political Affairs and Special Representative of Secretary-General Waldheim for Cyprus and Afghanistan. Through his mediation efforts, Mr. Pérez de Cuéllar contributed significantly to resolving the conflicts in Central America and defusing the war between Iran and Iraq. It was a happy coincidence that during his ten-year mandate, a number of sources of tension associated with the cold war were gradually eliminated.

Boutros Boutros-Ghali of Egypt served one five-year term as the sixth Secretary-General, from 1992 to 1996. Before his appointment, he had held a number of important functions, including as Minister of State for Foreign Affairs. He had a role in the negotiation of the Camp David Accords between Egypt and Israel, which were signed in 1979. From the very beginning of his mandate, Mr. Boutros-Ghali was set on reform. He submitted to the General Assembly a number of important proposals in the political and economic fields, including his "Agenda for Peace", and advocated inter alia measures of preventive diplomacy.

Kofi Annan of Ghana joined the United Nations system in 1962. Before becoming the seventh Secretary-General-serving two terms, from 1 January 1997 to 31 December 2006-he had already 35 years of United Nations experience, which culminated with the post of Under-Secretary-General for Peacekeeping Operations. When he became Secretary-General, his first major initiative was his plan for reform, "Renewing the United Nations", which he presented to the General Assembly as early as 1997. In 2000, he issued a Millennium report, which served as a basis for the Millennium Declaration adopted by Heads of State or Government in September 2000.

Throughout his ten-year mandate, Mr. Annan was committed to the process of reform. He often extended his good offices to deal with delicate political issues and on many solemn occasions he communicated with the leaders of the world from the rostrum of the General Assembly. Indeed, he often broke with tradition by leaving his seat at the top of the podium and going down a few steps to deliver his message, standing at the rostrum like all the other speakers.

Ban Ki-moon, former Minister for Foreign Affairs of the Republic of Korea, was appointed by the General Assembly as the eighth Secretary-General on 13 October 2006. He has had long-standing ties with the United Nations, dating back to 1975. He took the oath of office in the General Assembly Hall on 14 December, and on that occasion, he already created a precedent by placing his left hand on the UN Charter while taking the oath.

Mr. Ban warmly praised Kofi Annan for his achievements. Then, looking towards the future, he said inter alia: "By strengthening the three pillars of the United Nations-security, development and human rights-we can build a more peaceful, more prosperous and more just world for our succeeding generations. As we pursue our collective endeavour to reach that goal, my first priority will be to restore trust. I will seek to act as a harmonizer and bridge builder. And I hope to become known to all of you-Member States or Secretariat-as a Secretary-General, who is accessible, hard-working and prepared to listen attentively." Mr. Secretary-General, we have been inspired by your words and we all eagerly look forward to supporting you in your many challenging tasks.