George Mason IV (December 11, 1725 - October 7, 1792) was a United States patriot, statesman, and delegate from Virginia to the U.S. Constitutional Convention. He is called the "Father of the Bill of Rights". For all of these reasons he is considered to be one of the "Founding Fathers" of the United States. Mason wrote the Virginia Declaration of Rights, which detailed specific rights of citizens. In addition to anti-federalist Patrick Henry, he was later a leader of those who pressed for the addition of explicitly stated individual rights as part of the U.S. Constitution, and did not sign the document in part because it lacked such a statement. His efforts eventually succeeded in convincing the Federalists to modify the Constitution and add the Bill of Rights (the first ten amendments of the Constitution). The Bill of Rights is based on Mason's earlier Virginia Declaration of Rights.

Mason served at the Virginia Convention in Williamsburg in 1776. During this time he created drafts of the first declaration of rights and state constitution in the Colonies. Both were adopted after committee alterations; the Virginia Declaration of Rights was adopted June 12, 1776, and the Virginia Constitution was adopted June 29, 1776.

Mason was appointed in 1786 to represent Virginia as a delegate to a Federal Convention, to meet in Philadelphia for the purpose of revising the Articles of Confederation. He served at the Federal Convention in Philadelphia from May to September 1787 and contributed significantly to the formation of the Constitution. "He refused to sign the Constitution, however, and returned to his native state as an outspoken opponent in the ratification contest." One objection to the proposed Constitution was that it lacked a "declaration of rights". As a delegate to Virginia's ratification convention, he opposed ratification without amendment. Among the amendments he desired was a bill of rights. This opposition, both before and during the convention, may have cost Mason his long friendship with his neighbor George Washington, and is probably a leading reason why George Mason became less well-known than other U.S. founding fathers in later years. On December 15, 1791, the U.S. Bill of Rights, based primarily on George Mason's Virginia Declaration of Rights, was ratified in response to the agitation of Mason and others.

At the convention he was one of the five most frequent speakers and he always spoke with confidence. He believed that slave trade should be abolished, even though he himself owned slaves; he believed in the disestablishment of the church; and he was a strong anti-federalist. He wanted a three-part government, but he also wanted very powerful state governments.

An important issue for him in the convention was the bill of rights. He didn't want the United States to be like England. He foresaw sectional strife and feared the power of government.

Mason died peacefully at his home, Gunston Hall, on October 7, 1792. Gunston Hall, located in Mason Neck, Virginia, is now a tourist attraction. The George Mason Memorial is located in East Potomac Park, Washington, D.C., near the Thomas Jefferson Memorial; it was dedicated on April 9, 2002. A major bridge connecting Washington, DC, to Virginia is officially named the George Mason Memorial Bridge (it is part of the 14th Street bridge complex). George Mason High School and George Mason University located in Fairfax, Virginia, is named in his honor, as are Mason County, Kentucky, Mason County, West Virginia and Mason County, Illinois.