Charles Timothy Hagel is an American military veteran and former politician who served as the 24th United States secretary of defense from 2013 to 2015 in the administration of Barack Obama. He previously served as chairman of the president's Intelligence Advisory Board from 2009 to 2013 and as a United States senator representing Nebraska from 1997 to 2009.

The United States secretary of defense (SecDef) is the head of the United States Department of Defense, the executive department of the U.S. Armed Forces, and is a high-ranking member of the federal cabinet. The secretary of defense's position of command and authority over the military is second only to that of the president of the United States, who is the commander-in-chief. This position corresponds to what is generally known as a defense minister in many other countries. The secretary of defense is appointed by the president with the advice and consent of the Senate, and is by custom a member of the Cabinet and by law a member of the National Security Council.