Nathan Clifford was an American statesman, diplomat and jurist.
He represented served as Speaker of the Maine House of Representatives and Attorney General of Maine before representing the state in the United States House of Representatives. He then served in the administration of President James K. Polk as Attorney General and Ambassador to Mexico. In the latter office, he signed the Treaty of Guadeloupe Hidalgo. His career culminated in a lengthy service as an Associate Justice of the Supreme Court of the United States.
Clifford is one of only a handful of people who have served in all three branches of the U.S. federal government.