Dag Hjalmar Agne Carl Hammarskjöld; 29 July 1905 – 18 September 1961) was a Swedish diplomat, economist, and author, who served as the second Secretary-General of the United Nations, from April 1953 until his death in a plane crash in September 1961. At the age of 56 years and 255 days, Hammarskjöld was the youngest to have held the post. Additionally, he is one of only four people to be awarded a posthumous Nobel Prize and was the only United Nations Secretary-General to die while in office. He was killed in a Douglas DC-6 airplane crash en route to cease-fire negotiations. Hammarskjöld has been referred to as one of the two best secretaries-general, 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.
More information on the English and Swedish Wikipedia pages. The Nobel Prize page is [1].