U Thant was United Nations Secretary-General from 1961 to 1971.  He dealt with the top issues of the day, from the Cuban Missile Crisis to the Vietnam War and the Six Day War, meeting often with world leaders including John F. Kennedy, Nikita Khrushchev, Charles de Gaulle, Jawaharlal Nehru and Fidel 
Castro.  He was also a passionate believer in safeguarding the natural environment.