James Madison (March 16, 1751 [O.S. March 5, 1750] – June 28, 1836) was an American statesman, diplomat, and Founding Father who served as the fourth president of the United States from 1809 to 1817. Madison was popularly acclaimed as the "Father of the Constitution" for his pivotal role in drafting and promoting the Constitution of the United States and the Bill of Rights.

Madison was born into a prominent slave-owning planter family in Virginia. In 1774, strongly opposed to British taxation, Madison joined with the Patriots. He was a member of both the Virginia House of Delegates and the Continental Congress during and after the American Revolutionary War. Dissatisfied with the weak national government established by the Articles of Confederation, he helped organize the Constitutional Convention, which produced a new constitution designed to strengthen republican government against democratic assembly. Madison's Virginia Plan was the basis for the convention's deliberations. He became one of the leaders in the movement to ratify the Constitution and joined Alexander Hamilton and John Jay in writing The Federalist Papers, a series of pro-ratification essays that remain prominent among works of political science in American history.

Madison emerged as an important leader in the House of Representatives and was a close adviser to President George Washington. During the early 1790s, Madison opposed the economic program and the accompanying centralization of power favored by Secretary of the Treasury Hamilton. Alongside Thomas Jefferson, he organized the Democratic–Republican Party in opposition to Hamilton's Federalist Party. Madison served as Jefferson's Secretary of State from 1801 to 1809, during which time he helped convince Jefferson to submit the Louisiana Purchase Treaty for approval by the Senate.

Madison was elected president in 1808. Motivated by a desire to acquire land held by Britain, Spain, and Native Americans, and after diplomatic protests with a trade embargo failed to end British seizures of American-shipped goods, Madison led the United States into the War of 1812. Madison was re-elected in the 1812 election, which was held during wartime. The war convinced Madison of the necessity of a stronger federal government. Although the war ended inconclusively in 1815, many Americans viewed it as a successful "second war of independence" against Britain which bolstered Madison's popularity. He presided over the creation of the Second Bank of the United States and the enactment of the protective Tariff of 1816. The United States acquired 26×10^⁶ acres (110,000 km²) of land through treaties or war from Native American tribes during Madison's presidency.

Retiring from public office at the end of his presidency in 1817, Madison returned to his plantation, Montpelier, where he died in 1836. Madison was a slave owner; he freed one slave in 1783 to prevent a slave rebellion at Montpelier but did not free any in his will. Historians regard Madison as one of the most significant Founding Fathers of the United States, and have generally ranked him as an above-average president, although they are critical of his endorsement of slavery and his leadership during the War of 1812. Madison's name is commemorated in many landmarks across the nation, with prominent examples including Madison Square Garden, James Madison University, the James Madison Memorial Building, the capital city of Wisconsin, and the USS James Madison.

James Madison was born on March 16, 1751 (March 5, 1750, Old Style), at the Belle Grove plantation near Port Conway in the Colony of Virginia, to James Madison Sr. and Eleanor Madison. His family had lived in Virginia since the mid-17th century. Madison's maternal grandfather, Francis Conway, was a prominent planter and tobacco merchant. His father was a tobacco planter who grew up on a plantation, then called Mount Pleasant, which he inherited upon reaching adulthood. With an estimated 100 slaves and a 5,000-acre (2,000 ha) plantation, Madison's father was among the largest landowners in Virginia's Piedmont.

In the early 1760s, the Madison family moved into a newly built house that they named Montpelier. Madison was the oldest of twelve children, with seven brothers and four sisters, though only six lived to adulthood: brothers Francis, Ambrose, and William, and sisters Nelly, Sarah, and Frances. Ambrose helped to manage Montpelier for his father and older brother until he died in 1793.

From ages 11 to 16, Madison studied under Donald Robertson, a tutor for several prominent Southern families. Madison learned mathematics, geography, and modern and classical languages, becoming exceptionally proficient in Latin. At age 16, Madison returned to Montpelier, where he studied under the Reverend Thomas Martin to prepare for college. Unlike most college-bound Virginians of his day, Madison did not attend the College of William and Mary, as the lowland Williamsburg climate—thought to be more likely to harbor infectious disease—might have impacted his health. Instead, in 1769, he enrolled at the College of New Jersey (later Princeton University).