U Thant (Burma, now Myanmar) Term of Office: 1961-1971

U Thant served as Secretary-General of the United Nations from 1961 to 1971. He was chosen to head the world body when Secretary-General Dag Hammarskjöld was killed in an air crash in September 1961. 

U Thant was born in Pantanaw, Burma, on 22 January 1909. Prior to his diplomatic career, U Thant's experience was in education and information work. At the time of his appointment as Acting Secretary-General of the United Nations, U Thant had been Permanent Representative of Burma to the United Nations, with the rank of Ambassador (1957-1961). 

U Thant retired at the end of his second term in 1971, and he died on 25 November 1974, after a long illness.