Robert Goodloe Harper (January 1765 – January 14, 1825), a Federalist, was a member of the United States Senate from Maryland, serving from January 1816 until his resignation in December of the same year. He also served in the South Carolina House of Representatives (1790–1795), the U.S. House of Representatives from South Carolina (1795–1801), and in the Maryland State Senate. He is best remembered for the phrase, "Millions for defense, but not one cent for tribute" in connection with the XYZ Affair. The town of Harper, Liberia, is named after him.