Dag Hjalmar Agne Carl Hammarskjöld (Swedish: [dɑːɡ ˈhamːarɧœld] ( ); 29 July 1905 – 18 September 1961) was a Swedish diplomat, economist, and author. The second Secretary-General of the United Nations, he served from April 1953 until his death in a plane crash in September 1961. At the age of 47 years, 255 days, Hammarskjöld is the youngest to have held the post. He is one of just three people to be awarded a posthumous Nobel Prize. Hammarskjöld is the only U.N. Secretary-General to die in office; his death occurred en route to cease-fire negotiations. American President John F. Kennedy called Hammarskjöld "the greatest statesman of our century".[2]