Thomas Jefferson (April 13 [O.S. April 2], 1743 – July 4, 1826) was an American Founding Father and the third president of the United States from 1801 to 1809. He was the primary author of the Declaration of Independence. Jefferson was the nation's first U.S. secretary of state under George Washington and then the nation's second vice president under John Adams. Jefferson was a leading proponent of democracy, republicanism, and natural rights, and he produced formative documents and decisions at the state, national, and international levels.

Jefferson was born into the Colony of Virginia's planter class, dependent on slave labor. During the American Revolution, Jefferson represented Virginia in the Second Continental Congress, which unanimously adopted the Declaration of Independence. Jefferson's advocacy for individual rights, including freedom of thought, speech, and religion, helped shape the ideological foundations of the revolution. This inspired the Thirteen Colonies in their revolutionary fight for independence, which culminated in the establishment of the United States as a free and sovereign nation.

Jefferson served as the second governor of revolutionary Virginia from 1779 to 1781. In 1785, Congress appointed Jefferson as U.S. Minister to France, where he served from 1785 to 1789. President Washington then appointed Jefferson the nation's first secretary of state, where he served from 1790 to 1793. In 1792, Jefferson and political ally James Madison organized the Democratic-Republican Party to oppose the Federalist Party during the formation of the nation's First Party System. Jefferson and Federalist John Adams became both personal friends and political rivals. In the 1796 U.S. presidential election between the two, Jefferson came in second, which made him Adams' vice president under the electoral laws of the time. Four years later, in the 1800 presidential election, Jefferson again challenged Adams and won the presidency. In 1804, Jefferson was reelected overwhelmingly to a second term, crushing his main opposition, the Federalist's Charles Cotesworth Pinckney of South Carolina.

Jefferson's presidency assertively defended the nation's shipping and trade interests against Barbary pirates and aggressive British trade policies, promoted a western expansionist policy with the Louisiana Purchase, which doubled the nation's geographic size, and reduced military forces and expenditures following successful negotiations with France. In his second presidential term, Jefferson was beset by difficulties at home, including the trial of his former vice president Aaron Burr. In 1807, Jefferson implemented the Embargo Act to defend the nation's industries from British threats to U.S. shipping, limit foreign trade, and stimulate the birth of the American manufacturing.

Jefferson is ranked among the upper tier of U.S. presidents both by scholars and in public opinion. Presidential scholars and historians have praised Jefferson's advocacy of religious freedom and tolerance, his peaceful acquisition of the Louisiana Territory from France, and his leadership in supporting the Lewis and Clark Expedition. They acknowledge his lifelong ownership of large numbers of slaves, but offer varying interpretations of his views on and relationship with slavery.

Jefferson was born on April 13, 1743 (April 2, 1743, Old Style, Julian calendar), at the family's Shadwell Plantation in the Colony of Virginia, then one of the Thirteen Colonies of British America. He was the third of ten children. His father, Peter Jefferson, was a planter and surveyor; his mother was Jane Randolph. Peter Jefferson moved his family to Tuckahoe Plantation in 1745 following the death of William Randolph III, the plantation's owner and Jefferson's friend, who in his will had named Peter guardian of Randolph's children. The Jeffersons returned to Shadwell before October 1753.

Jefferson began his education together with the Randolph children at Tuckahoe under tutors. Thomas' father Peter, who was self-taught and regretted not having a formal education, entered Thomas into an English school at age five. In 1752, at age nine, he attended a local school run by a Presbyterian minister and also began studying the natural world, which he grew to love. He studied Latin, Greek, and French, and began learning to ride horses. Thomas read books from his father's modest library. He was taught from 1758 to 1760 by the Reverend James Maury near Gordonsville, Virginia, where he studied history, science, and the classics while boarding with Maury's family. Jefferson came to know various American Indians, including Cherokee chief Ostenaco, who often stopped at Shadwell to visit on their way to Williamsburg to trade. In Williamsburg, the young Jefferson met and came to admire Patrick Henry.

Thomas's father died in 1757, and his estate was divided between his sons, Thomas and Randolph. John Harvie Sr. became 14-year-old Thomas' guardian. Thomas inherited approximately 5,000 acres (7.8 sq mi; 20.2 km²), which included the land on which he later built Monticello in 1772.