Aaron Burr, Jr. (6 February 1756 - 14 September 1836) was an American politician, Revolutionary War hero and adventurer. He served as the third Vice President of the United States under Thomas Jefferson (1801-1805). Burr famously killed Alexander Hamilton in a duel.

A formative member of the Democratic-Republican Party with a political base in New York, Burr served in the New York State Assembly (1784-1785, 1798-1801), as New York State Attorney General (1789-1791), United States Senator (1791-1797), and for one term as Vice President of the United States (1801-1805) under President Thomas Jefferson. A candidate for President in 1800, Burr tied Jefferson with 73 electoral votes, making him eligible for one of the Nation's two highest offices and sending the election into the U.S. House of Representatives. After 36 ballots, Jefferson was elected President and Burr elected Vice President. As Vice President, Burr was President of the Senate, and in such role, presided over the impeachment trial of Samuel Chase.

During an unsuccessful campaign for election to Governor of New York in 1804, Burr was often referred to in published articles written by Alexander Hamilton (1755-1804), a long-time political rival and son-in-law of Philip Schuyler, the first U.S. Senator from New York who Burr defeated in his bid for re-election in 1791. Taking umbrage at remarks made by Hamilton at a dinner party and Hamilton's subsequent failure to account for the remarks, Burr challenged Hamilton to a duel on 11 July 1804, at the Heights of Weehawken in New Jersey at which he mortally wounded Hamilton. Arguably the most famous duel in U.S. history, it had immense political ramifications. Burr, who survived the duel, was indicted for murder in both New York and New Jersey (though these charges were either later dismissed or resulted in acquittal), and the harsh criticism and animosity directed towards him brought about an end to his political career in the East, though he remained a popular figure in the West and South. Further, Hamilton's untimely death would fatally weaken the fledging remnants of the Federalist Party, which, given the death of George Washington (1732-1799) five years earlier, was left without a strong leader.

After Burr left the Vice Presidency at the end of his term in 1805, he journeyed into what was then the U.S. West, particularly the Ohio River Valley area and the lands acquired in the Louisiana Purchase. While historians are uncertain as to Burr's particular activities, he was accused in turns of having committed treason, of a conspiracy to steal Louisiana Purchase lands away from the United States and crown himself a King or Emperor, or of an attempt to declare an illegal war against Spanish possessions in Mexico. He did go so far as to form his own regiment of at least 200 men. Burr was arrested in 1807 and brought to trial on charges of treason, for which he was acquitted. After several years in self-imposed exile in Europe, Burr returned to practicing law in New York City and lived a largely reclusive existence until his death.