Thomas W. Harker is an American government official who has served in the United States Department of Veterans Affairs and the United States Department of Defense. Harker was nominated by President Donald Trump to serve as an assistant secretary of the Navy and was confirmed on December 20, 2017 and sworn in on January 2, 2018. He was designated as the acting United States under secretary of defense (comptroller) on June 26, 2020.

The Under Secretary of Defense (Comptroller)/Chief Financial Officer, abbreviated USD(C)/CFO, is a high level civilian official in the United States Department of Defense. The Under Secretary of Defense (Comptroller) is the principal staff assistant and adviser to both the Secretary of Defense and the Deputy Secretary of Defense for all budgetary and fiscal matters, including the development and execution of the Defense Department's annual budget.