Thomas Jefferson (April 13, 1743 - July 4, 1826) was an American statesman, diplomat, lawyer, architect, philosopher, and founding father who served as the third President of the United States from 1801 to 1809. He previously served as Second Vice President. from the United States from 1797 to 1801. The lead author of the Declaration of Independence, Jefferson was an advocate of democracy, republicanism, and individual rights, prompting American settlers to break with the Kingdom of Great Britain and form a new nation; produced formative documents and decisions at both the state and national levels.

During the American Revolution, he represented Virginia in the Continental Congress that adopted the Declaration, drafted the Religious Liberty Act as a Virginia legislator, and served as Virginia's second Governor from 1779 to 1781, during the American Revolutionary War. He became the Minister of the United States in France in May 1785, and subsequently the country's first secretary of state under President George Washington from 1790 to 1793. Jefferson and James Madison organized the Democratic-Republican Party to oppose the Federalist Party during the formation of the First Party System. With Madison, he wrote anonymously the provocative Kentucky and Virginia Resolutions in 1798 and 1799, which sought to strengthen the rights of states by nullifying federal Aliens and Sedition Laws.

As President, Jefferson pursued the nation's shipping and trading interests against Barbary pirates and aggressive British trade policies. Beginning in 1803, Jefferson promoted a western expansionist policy, organizing the Louisiana Purchase, doubling the nation's land area. To make room for the white settlements, Jefferson began a controversial process of Indian tribal expulsion from the newly acquired territory. As a result of the peace negotiations with France, his administration reduced the military forces. Jefferson was reelected in 1804. His second term was fraught with difficulties at home, including the trial of former Vice President Aaron Burr. In 1807, US foreign trade declined when Jefferson implemented the Garnishment Act in response to British threats to the US shipments. The same year, Jefferson signed the Law that prohibits the importation of slaves. After retiring from public office, he founded the University of Virginia.

Jefferson, although primarily a planter, lawyer, and politician, mastered many disciplines, ranging from surveying and mathematics to horticulture and mechanics. He was an architect in the classical tradition. Jefferson's keen interest in religion and philosophy led him to the presidency of the American Philosophical Society; he rejected organized religion but was influenced by Christianity and deism. A philologist, Jefferson knew several languages. He was a prolific letter writer and corresponded with many prominent people. His only complete book is Notes on the State of Virginia (1785), considered perhaps the most important American book published before 1800.