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 7.00147E+18 47 years, 7.00226E+18 255 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".