Dag Hjalmar Agne Carl Hammarskjöld (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. He is the only person to have been awarded a posthumous Nobel Peace Prize. Hammarskjöld remains the only U.N. Secretary-General to die in office, and his death occurred en route to cease-fire negotiations. American President John F. Kennedy called Hammarskjöld “the greatest statesman of our century".