John Adams (October 30, 1735 – July 4, 1826) was an American statesman, attorney, diplomat, writer, and Founding Father who was the second president of the United States, serving from 1797 to 1801. Before his presidency, he was a leader of the American Revolution that achieved independence from Great Britain, and he served as the first vice president of the United States from 1789 to 1797. Adams was a dedicated diarist and regularly corresponded with many important figures in early American history, including his wife and adviser Abigail Adams and Thomas Jefferson.

A lawyer and political activist prior to the revolution, Adams was devoted to the right to counsel and presumption of innocence. He defied anti-British sentiment and successfully defended British soldiers against murder charges arising from the Boston Massacre. Adams was a Massachusetts delegate to the Continental Congress and became a leader of the revolution. He assisted in drafting the Declaration of Independence in 1776. As a diplomat in Europe, he helped negotiate a peace treaty with Great Britain and secured vital governmental loans. Adams was the primary author of the Massachusetts Constitution in 1780, which influenced the United States constitution, as did his essay Thoughts on Government.

Adams was elected to two terms as vice president under President George Washington and was elected as the United States' second president in 1796. He was the only president elected under the banner of the Federalist Party. During his single term, Adams encountered fierce criticism from the Jeffersonian Republicans and from some in his own Federalist Party, led by his rival Alexander Hamilton. Adams signed the controversial Alien and Sedition Acts and built up the Army and Navy in the undeclared Quasi-War with France. During his term, he became the first president to reside in the executive mansion now known as the White House.

In his bid for reelection, opposition from Federalists and accusations of despotism from Jeffersonians led to Adams losing to his vice president and former friend Jefferson, and he retired to Massachusetts. He eventually resumed his friendship with Jefferson by initiating a correspondence that lasted fourteen years. He and his wife generated a family of politicians, diplomats, and historians now referred to as the Adams political family, which includes their son John Quincy Adams, the sixth president of the United States. John Adams died on July 4, 1826 – the fiftieth anniversary of the adoption of the Declaration of Independence – hours after Jefferson's death. Adams and his son are the only presidents of the first twelve that did not own slaves in their lives. Surveys of historians and scholars have favorably ranked his administration.