George Mason IV (December 11, 1725 – October 7, 1792) was an American Patriot, statesman and a delegate from Virginia to the U.S. Constitutional Convention. Along with James Madison, he is called the "Father of the Bill of Rights." For these reasons he is considered one of the "Founding Fathers" of the United States.

Like anti - federalist Patrick Henry, Mason was a leader of those who pressed for the addition of explicit States rights and individual rights to the U.S. Constitution as a balance to the increased federal powers, and did not sign the document in part because it lacked such a statement. His efforts eventually succeeded in convincing the Federalists to add the first ten amendments of the Constitution. These amendments, collectively known as the Bill of Rights, were based on the earlier Virginia Declaration of Rights, which Mason had drafted in 1776. On the nagging issue of slavery, Mason walked a fine line. Although a slaveholder himself, he found slavery repugnant for a variety of reasons. He wanted to ban further importation of slaves from Africa and prevent slavery from spreading to more states. However, he did not want the new federal government to be able to ban slavery where it already existed, because he anticipated that such an act would be difficult and controversial.

George Mason was born on December 11, 1725 to George and Ann Thomson Mason at the Mason family plantation in Fairfax County, Virginia. His father died in 1735 in a boating accident on the Potomac, when the boat capsized and he drowned. After this event the younger Mason lived with his uncle John Mercer. On April 4, 1750, he married sixteen year old Ann Eilbeck, from a plantation in Charles County, Maryland. They lived in a house on his property in Dogue's Neck, Virginia. Mason completed construction of Gunston Hall, a plantation house on the Potomac River, in 1759. He and his wife had twelve children, nine of whom survived to adulthood. George Mason's last two children were James and Richard Mason; twins who were born in December, 1772 but died six weeks later. Their mother died three months later on March 9, 1773 due to complications. George Mason remarried on April 11, 1780 but did not have any children with his new wife, Sarah Brent. George Mason also suffered from the condition known as gout for a large part of his life, and in accordance with current medical treatment, relied upon bloodletting.

Mason had virtually no formal schooling and essentially educated himself from his uncle's library. 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, Mason was one of the five most frequent speakers. Mason believed in the disestablishment of the church. Mason was a strong anti - federalist who wanted a weak central government, divided into three parts, with little power, leaving the several States with a preponderance of political power.

An important issue for him in the convention was the Bill of Rights. He did not want the United States to be like England. He foresaw sectional strife and feared the power of government.

A Virginia planter, Mason owned many African slaves. Like some of his contemporary slave owners (e.g. Thomas Jefferson and George Washington), Mason conceded that the institution was morally objectionable, once calling it a "slow Poison" that "is daily contaminating the Minds & Morals of our People." Mason favored the abolition of the slave trade, but he did not advocate for the immediate abolition of slavery. Like Jefferson, he owned slaves whom he did not manumit.

Two of Mason's stated reasons for opposing the U.S. Constitution were seemingly contradictory: on the one hand, he said that the draft Constitution did not specifically protect the right of states to let slavery continue where it already existed, and on the other hand he also said that the draft Constitution did not allow Congress to immediately stop the importation of slaves. Mason's immediate concern was to prevent more slaves from being imported, and to prevent slavery from spreading into more states. He was not eager to ban slavery where it already existed: "It is far from being a desirable property. But it will involve us in great difficulties and infelicity to be now deprived of them." Mason ostensibly balanced his anti - slavery argument that importation should stop, with a pro-slavery argument that the draft Constitution should protect slavery from being taxed out of existence; however, the latter argument had already been incorporated into the Constitution according to James Madison.

Because of his efforts to stop the spread of slavery, and his recognition of the undesirability of slavery, some historians have said that Mason should be categorized as an abolitionist. Other historians have disagreed.

George Mason died peacefully at his home, Gunston Hall, on October 7, 1792. Gunston Hall, located in Mason Neck, Virginia, is now a museum and tourist attraction. The George Mason Memorial in West Potomac Park, Washington, D.C., near the Thomas Jefferson Memorial, was dedicated on April 9, 2002. The George Mason Memorial Bridge, one of five that make up the 14th Street Bridge, connects Washington, D.C. to Virginia. George Mason Elementary School in Alexandria, Virginia, George Mason High School in Falls Church, Virginia, and George Mason University in Fairfax, Virginia, are named in his honor, as are Mason County, Kentucky, Mason County, West Virginia, and Mason County, Illinois. He was honored by the United States Postal Service with an 18¢ Great Americans series postage stamp. A bas-relief of Mason appears in the Chamber of the U.S. House of Representatives as one of 23 honoring great lawmakers; his image is located above and to the right of the Speaker's chair.