Aaron Burr Jr. (February 6, 1756 September 14, 1836) was an American politician and lawyer who served as the third vice president of the United States from 1801 to 1805. Burr's legacy is defined by his famous personal conflict with Alexander Hamilton that culminated in Burr killing Hamilton in a duel in 1804, while Burr was vice president.

Burr was born to a prominent family in New Jersey. After studying theology at Princeton, he began his career as a lawyer before joining the Continental Army as an officer in the American Revolutionary War in 1775. After leaving military service in 1779, Burr practiced law in New York City, where he became a leading politician and helped form the new Jeffersonian Democratic-Republican Party. As a New York Assemblyman in 1785, Burr supported a bill to end slavery, despite having owned slaves himself.At age 26, Burr married Theodosia Bartow Prevost, who died in 1794 after twelve years of marriage. They had one daughter, Theodosia.

In 1791, Burr was elected to the U.S. Senate, where he served until 1797. Burr would later run as the Democratic-Republican vice-presidential candidate in the 1800 election. An unintentional electoral college tie between Burr and presidential candidate Thomas Jefferson resulted in the House of Representatives voting in Jefferson's favor, with Burr becoming Jefferson's vice president due to receiving the second-highest share of the votes. Although Burr maintained that he supported Jefferson, the president was highly suspicious of Burr, who was relegated to the sidelines of the administration during his vice presidency and not re-nominated as Jefferson's running mate in 1804.

During his last year as vice president, Burr engaged in the duel in which he fatally shot Hamilton, his political rival, near where Hamilton's son Philip Hamilton died three years prior. Although dueling was illegal, Burr was never tried, and all charges against him were eventually dropped. Nevertheless, Hamilton's death ended Burr's political career.

Burr traveled west to the American frontier, seeking new economic and political opportunities. His secretive activities led to his 1807 arrest in Alabama on charges of treason. He was brought to trial more than once for what became known as the Burr conspiracy, an alleged plot to create an independent country led by Burr, but was acquitted each time. With large debts and few influential friends, Burr left the United States to live as an expatriate in Europe. He returned in 1812 and resumed practicing law in New York City. Burr's brief second marriage resulted in divorce and further scandal. Handicapped by a stroke and financially ruined, Burr died at a boarding house in 1836.

The vice president of the United States (VPOTUS) is the second-highest officer in the executive branch of the U.S. federal government, after the president of the United States, and ranks first in the presidential line of succession. The vice president is also an officer in the legislative branch, as the president of the Senate. In this capacity, the vice president is empowered to preside over Senate deliberations at any time, but may not vote except to cast a tie-breaking vote. The vice president is indirectly elected together with the president to a four-year term of office by the people of the United States through the Electoral College.The modern vice presidency is a position of significant power and is widely seen as an integral part of a president's administration. While the exact nature of the role varies in each administration, most modern vice presidents serve as a key presidential advisor, governing partner, and representative of the president. The vice president is also a statutory member of the National Security Council and thus plays a significant role in national security matters. As the vice president's role within the executive branch has expanded, the legislative branch role has contracted; for example, vice presidents now preside over the Senate only infrequently.The role of the vice presidency has changed dramatically since the office was created during the 1787 Constitutional Convention. Originally something of an afterthought, the vice presidency was considered an insignificant office for much of the nation's history, especially after the Twelfth Amendment meant that vice presidents were no longer the runners-up in the presidential election. The vice president's role began steadily growing in importance during the 1930s, with the Office of the Vice President being created in the executive branch in 1939, and has since grown much further. Due to its increase in power and prestige, the vice presidency is now often considered to be a stepping stone to the presidency. Since the 1970s, the vice president has been afforded an official residence at Number One Observatory Circle.

The Constitution does not expressly assign the vice presidency to a branch of the government, causing a dispute among scholars about which branch the office belongs to (the executive, the legislative, both, or neither). The modern view of the vice president as an officer of the executive branch—one isolated almost totally from the legislative branch—is due in large part to the assignment of executive authority to the vice president by either the president or Congress. Nevertheless, modern vice presidents have often previously served in Congress, and are often tasked with helping to advance an administration's legislative priorities.

Kamala Harris is the 49th and current vice president of the United States. She is the first African American, first Asian American, and first female occupant of the office. She assumed office on January 20, 2021.