Dag Hjalmar Agne Carl Hammarskjöld ( HAM-ər-shuuld, Swedish: [ˈdɑːɡ ˈhâmːarˌɧœld] (listen); 29 July 1905 – 18 September 1961) was a Swedish economist and diplomat who served as the second Secretary-General of the United Nations. As of 2021, Hammarskjöld remains the youngest person to have held the Secretary-General post, having been only 47 years old when he was appointed in 1953. His second term was cut short when he died in the crash of his DC-6 airplane in Northern Rhodesia while en route to cease-fire negotiations during the Congo Crisis. He is the only person in history to be awarded a Nobel Peace Prize posthumously.
Hammarskjöld has been referred to as one of the two best secretaries-general of the United Nations, and his appointment has been mentioned as the most notable success for the UN. US President John F. Kennedy called Hammarskjöld "the greatest statesman of our century."