Hugh McCulloch was an American financier who played a central role in financing the American Civil War. He served two non-consecutive terms as U.S. Treasury Secretary under three presidents. He was originally opposed to the creation of a system of national banks, but his reputation as head of the Bank of Indiana from 1857 to 1863 persuaded the Treasury to bring him in to supervise the new system as Comptroller of the Currency 1863–1865. As Secretary of the Treasury 1865–1869 he reduced and funded the gigantic Civil War debt of the union, and reestablished the federal taxation system across the former Confederate States of America. He tried but failed to make a rapid return to the gold standard.

The United States secretary of the treasury is the head of the United States Department of the Treasury, and is the chief financial officer of the federal government of the United States. The secretary of the treasury serves as the principal advisor to the president of the United States on all matters pertaining to economic and fiscal policy. The secretary is, by custom, a member of the president's cabinet and, by law, a member of the National Security Council.