George Mason (December 11, 1725 [O.S. November 30, 1725] – October 7, 1792) was an American planter, politician, Founding Father, and delegate to the U.S. Constitutional Convention in Philadelphia in 1787, where he was one of three delegates who refused to sign the Constitution. His writings, including substantial portions of the Fairfax Resolves of 1774, the Virginia Declaration of Rights of 1776, and his Objections to this Constitution of Government (1787) opposing ratification, have exercised a significant influence on American political thought and events. The Virginia Declaration of Rights, which Mason principally authored, served as a basis for the United States Bill of Rights, of which he has been deemed a father.

Mason was born in 1725 in present-day Fairfax County, Virginia. His father drowned when a storm capsized his boat while crossing the Potomac River in 1735 when Mason was about nine years old. His mother managed the family estates until he came of age. In 1750, Mason married, built Gunston Hall, and lived the life of a country squire, supervising his lands, family, and slaves. He briefly served in the House of Burgesses and involved himself in community affairs, sometimes serving with his neighbor George Washington. As tensions grew between Great Britain and the North American colonies, Mason came to support the colonial side, using his knowledge and experience to help the revolutionary cause, finding ways to work around the Stamp Act 1765 and serving in the pro-independence Fourth Virginia Convention in 1775 and the Fifth Virginia Convention in 1776.

Mason prepared the first draft of the Virginia Declaration of Rights in 1776, and his words formed much of the text adopted by the final Revolutionary Virginia Convention. He also wrote a constitution for the state; Thomas Jefferson and others sought to have the convention adopt their ideas, but Mason's version was nonetheless adopted. During the American Revolutionary War, Mason was a member of the powerful House of Delegates of the Virginia General Assembly, but to the irritation of Washington and others, he refused to serve in the Second Continental Congress in Philadelphia, citing health and family commitments.

In 1787, Mason was named one of his state's delegates to the Constitutional Convention in Philadelphia, his only lengthy trip outside Virginia. Many clauses in the Constitution were influenced by Mason's input, but he ultimately did not sign the final version, citing the lack of a bill of rights among his most prominent objections. He also wanted an immediate end to the slave trade and a supermajority requirement for navigation acts, fearing that restrictions on shipping might harm Virginia. He failed to attain these objectives in Philadelphia and later at the Virginia Ratifying Convention of 1788. His prominent fight for a bill of rights led fellow Virginian James Madison to introduce the same during the First Congress in 1789; these amendments were ratified in 1791, a year before Mason died. Obscure after his death, Mason later came to be recognized in the 20th and 21st centuries for his contributions to Virginia and the early United States.

Mason was born in present-day Fairfax County, in the Colony of Virginia, in British America, on December 11, 1725. Mason's parents owned property in Mason Neck, Virginia and a second property across the Potomac River in Maryland, which had been inherited by his mother.

Mason's great-grandfather George Mason I was a Cavalier who was born in 1629 in Pershore, Worcestershire, England. Militarily defeated in the English Civil War, Mason and other Cavaliers emigrated to the American colonies in the 1640s and 1650s. Mason I settled in present-day Stafford County, Virginia, where he was awarded land as a reward for bringing his family and servants to the Colony of Virginia, under headright, which awarded 50 acres for each person transported into the Colony. His son, George Mason II (1660–1716), was the first to move to what in 1742 became Fairfax County, then at the frontier between English and Native American controlled areas. George Mason III (1690–1735) like his father and grandfather served in the House of Burgesses and also as county lieutenant. George Mason IV's mother, Ann Thomson Mason, was the daughter of a former Attorney General of Virginia who immigrated from England.

Colonial Virginia at the time had few roads, and boats carried most commerce on Chesapeake Bay or its tributaries, including the Potomac and Rappahannock rivers. Most settlement took place near the rivers, through which planters could trade with the world. Colonial Virginia initially had few towns, since estates were largely self-sufficient and could obtain what they needed without the need to purchase locally. Even the capital, Williamsburg, had limited economic activity when the legislature was not in session. Local politics was dominated by large landowners, including the Masons. The Virginia economy rose and fell with tobacco, the main crop, which was raised mostly for export to Great Britain.

In 1736, Mason began his education with a Mr. Williams, who was hired to teach Mason for the price of 1,000 pounds (450 kg) of tobacco per annum. His studies began at his mother's house. But the following year, he boarded with a Mrs. Simpson in Maryland, and Williams continued as his teacher through 1739. By 1740, Mason was at Chopawamsic, under the tutelage of a Dr. Bridges, likely Charles Bridges, who helped develop the British schools run by the Society for the Promotion of Christian Knowledge, and arrived in British America in 1731. Mason and his brother Thomson likely utilized John Francis Mercer's library, one of the largest in Virginia at the time. Conversations with Mercer and book-lovers who gathered around him could have continued his education informally.