Thomas Jefferson was the third President of the United States (1801–1809), author of the Declaration of Independence (1776), and one of the most influential founders of the United States. Major events during his presidency include the Louisiana Purchase (1803), the Embargo Act of 1807, and the Lewis and Clark Expedition (1804–1806).

A political philosopher who promoted classical liberalism, republicanism, and the separation of church and state, he was the author of the Virginia Statute for Religious Freedom (1779 - 1786), which was the basis of the Establishment Clause of the First Amendment of the U.S. Constitution. He was the eponym of Jeffersonian democracy and the founder and leader of the Democratic-Republican Party, which dominated American politics for over a quarter-century and was the precursor to today's Democratic Party. Jefferson also served as the second Governor of Virginia (1779–1781), first United States Secretary of State (1789–1795), and second Vice President (1797–1801).