William du Pont Jr. (February 11, 1896 – December 31, 1965) was an English-born American businessman and banker, and a prominent figure in the sport of Thoroughbred horse racing.

His older sister was Marion, and they grew up at Montpelier, the historic home of President James Madison, which their parents had bought and expanded.

Their marriage celebration in Rosemont, Pennsylvania, was billed as the "Wedding of the Century" in media accounts because of the wealth of each family.

The estate featured a Gothic Revival castle built in 1855, which du Pont had remodeled into another replica of his boyhood home of Montpelier.

That same year, du Pont was made chairman of the board at the Delaware Trust Company, retaining his position as president as well.

Their son William du Pont III also was active with thoroughbreds and later owned Pillar Stud in Lexington, Kentucky.

[2] In 1927, du Pont imported Satrap from England and brought the son of The Tetrarch to stand at his second facility, the new Walnut Hall Farm near Boyce, Virginia.

[7] In 1936, duPont was part of the syndicate that bought and imported the stallion Blenheim, Aga Khan's Epsom Derby winner.

During this time, du Pont won the 1938 Preakness Stakes with Dauber, the second race of the Triple Crown for three-year-olds.

Located four miles (6 km) south of Orange, Virginia, the estate had been the plantation home of James Madison, fourth President of the United States.

[10] The National Trust acquired the property to preserve and interpret as a public history site for James and Dolley Madison, his presidency, and the architecture and society of Montpelier.

Following a widely publicized scandal in which the Trust fired all of its staff members who had been working towards increased representation of Americans descended from many James Madison's numerous slaves of African heritage on the estate's board of directors, the trust reached an agreement with the descendants group granting the group a majority of board seats, and has since that time been making efforts to reemphasize the history taught at the former plantation around the important historical context of James Madison's participation in slavery in the United States.

[11][12][13] Following du Pont's death, none of his heirs were interested in retaining the Bellevue Hall estate due to its extensive collection of recreational facilities and the upkeep they required.