Who is the Secretary of Defense?

The Secretary of Defense is the head of the Department of Defense and plays a critical role in defense policy and administration. As of the latest available information, Dr. Mark Esper served in this capacity, having been appointed in July 2019. The Secretary of Defense oversees the military and works with the President on national security matters, making key decisions regarding military strategy and operations.

The other individuals mentioned are significant figures within the military and defense apparatus. Ryan McCarthy served as the Secretary of the Army during a certain period, while General Dunford was the Chairman of the Joint Chiefs of Staff, focusing on military operations and advising the President and Secretary of Defense. General McConville is a current Chief of Staff of the Army, responsible for leading the Army and its operations but does not hold the position of Secretary of Defense. Thus, Dr. Mark Esper is the correct choice for this question based on his role and responsibilities during his tenure as Secretary of Defense.