1945: Gladwyn JebbThe first leader of the United Nations

Source: United Nations (video statements)

Gladwyn Jebb (Great Britain, 1900 – 1996) was made a Counsellor within the Foreign Office of Great Britain in 1943. It was in this position that he attended numerous international conferences, including the Conference on International Organization in San Francisco—which ultimately led to the birth of the United Nations. In 1945, Jebb served as the Executive Secretary of the Preparatory Commission of the United Nations. He was appointed as the United Kingdom’s Permanent Representative to the United Nations from 1950 to 1954.

https://www.youtube.com/watch?v=N3HxtevEUWI