Mark Esper is an American politician and former military officer who served as the 27th United States Secretary of Defense from July 2019 to November 2020. He was appointed by President Donald Trump and played a key role in shaping U.S. defense policy during his tenure, including issues related to NATO and military operations in Afghanistan. Before becoming Secretary of Defense, Esper held various positions in the U.S. Army and served as the Secretary of the Army. He has a background in both military service and public policy, having earned degrees from West Point and George Washington University.