Dag Hjalmar Agne Carl Hammarskjöld was a Swedish economist and diplomat who served as the second Secretary-General of the United Nations from April 1953 until his death in a plane crash in September 1961. As of 2026, he remains the youngest person to have held the post, having been only 47 years old when he was elected. He was a son of Hjalmar Hammarskjöld, who served as Prime Minister of Sweden from 1914 to 1917.