William du Pont (1855-1928) was an industrialist and member of the promienent du Pont family of Delaware, whose family business was the E.I. du Pont de Nemours & Company, also known as the DuPont Company which was a large manufacturer of gunpowder. He was the youngest son of Louisa Gerhard du Pont (1816-1900) and General Henry du Pont (1812-1889), who was the third president of the DuPont Company. From 1869 to 1872, William du Pont attended the Lake Mohegan boarding school in New York State, and in 1872, he was admitted to the Massachusetts Institute of Technology (MIT). However, he left MIT at the beginning of the 1873 spring semester due to medical problems with his eye.

William du Pont became involved in the family business in 1876. As an assistant to his father, DuPont Company president Henry du Pont, he managed the company's farms, developing skills instrumental in his future activities in horse and cattle breeding. His work in explosives manufacturing began in 1880, when he was appointed to help his cousin Lammot du Pont (1831-1884) in the first du Pont high explosives (dynamite) enterprise, Repauno Chemical Company. At first, William du Pont was the company's secretary and treasurer (1880-1884); then, after Lammot du Pont's tragic death on March 29, 1884, he became president from 1884 to 1892. At the same time, he performed treasurer and presidential duties for the Hercules Powder Company and the Torpedo Company, which were also associated with Lammot du Pont.

After his father died in 1889, he gave up his partnership in the DuPont Company and resigned from Repauno, Hercules and the Torpedo companies. In 1914, he returned for a short period of time to active duty as the director and the chairman of the Financial Committee of the E.I. du Pont de Nemours Powder Company. However, in March 1916, together with his cousin Alfred I. du Pont (1864-1935), he was expelled from the committee and the board due to their conflict with the company's new president, his coutsin Pierre S. du Pont (1870-1954). William du Pont's last involvement with the explosives industry was his investment and directorship, from 1919 through 1926, in the U.S. Flashless Powder Company (a.k.a. U.S.F. Powder Company), a company organized by his cousins Francis I. du Pont (1873-1942) and Ernest du Pont (1880-1944) to develop and manufacture powder for night gunfire.

In 1916, William du Pont, together with his cousin Alfred I. du Pont, bought the Delaware Trust Company. He remained affiliated with it for the next twelve years as its vice president (1916-1920), president (1920-1922), and chairman of the board (1923-1928). From 1917, he was on the board of directors of the United States Fidelity and Guarantee Company of Baltimore, also. His previous involvement in the banking business included service on the board of directors and on the Executive Committee of the Equitable Guarantee & Trust Company of Wilmington, Delaware in the late 1880s through the early 1890s.

As for his personal life, in 1878, William du Pont married his cousin May Lammot du Pont (1854-1927), the daughter of Victor du Pont (1828-1888) and Alice Hounsfield du Pont (1833-1904). The couple divorced in 1892 in South Dakota. He spent six month in that state in order to have residency for the divorce. In June 1892, he married Annie Rogers Zinn (1858-1927), the daughter of the locomotive maker Theodore Rogers (1829-1871) and Mary Andrews Rogers (1836-1918). Annie Rogers Zinn was the divorced wife of George Zinn (1842-1899) of New Castle, Delaware. William and Annie du Pont, alienated by the du Pont family and Wilmington society, left the United States and settled in Europe for ten years. The couple had two children: a daughter, Marion du Pont Somerville Scott (1894-1983) and a son, William du Pont Jr. (1896-1965), and supported a son from her previous marriage, George Zinn (1883-1929). While living in England, the family maintained their home at "Bellevue Hall" near Wilmington, and in 1900, purchased a home in Virginia named "Montpelier," formerly owned by the fourth President of the United States, James Madison. The family moved there in the beginning of 1902.

du Pont was affiliated through founding and board positions in the banking and railroad industry. He played a significant role in the American horse and cattle breeding industry. He performed judging duties at numerous horse shows around the country and financed prizes and awards. Also, he was a member of various hunting, yachting, and social clubs. As a member of the American Game Protective and Propagation Association, William du Pont worked in support of the Migratory Bird Treaty Act of 1918.

William du Pont died on January 20, 1928, at his estate Altama, near Brunswick, Georgia. His wife, Annie Rogers du Pont, had died in London a year earlier on January 22, 1927.

William du Pont, Jr. was the youngest child of William du Pont (1865-1928) and his second wife Annie Rogers Zinn du Pont (1858-1827). He was born on February 11, 1896, in Loseley Park, Guildford, Surrey County, England, where his parents lived from 1892 until 1902. His childhood was spent in England and then at Montpelier, Virginia, the estate purchased by William du Pont in 1902. This was the former residence of United States President James Madison. The family spent time at Bellevue, an estate north of Wilmington, Delaware, which William du Pont had inherited from his father Henry du Pont (1812-1889).

William du Pont, Jr. married Jean Liseter Austin (1897-1988) on January 1, 1919. The couple lived at Rosemont, near Newtown Square, Pennsylvania, where they built a house on land given to them as a wedding gift by Jean Austin's father William Liseter Austin. They had four children: Jean Ellen (born February 23, 1923), Evelyn Rebecca Austin du Pont (1925-1999), Henry Eleuthere Irenee du Pont (1927-2002; name legally changed from William Henry) and John Eleuthere du Pont (1938-2010). William du Pont, Jr. and Jean Austin du Pont separated in 1940 and were divorced in 1941. J. L. Austin du Pont continued to live at Rosemont while her husband moved to Bellevue Hall, which he had inherited from his father. It became his permanent residence for the rest of his life.

William du Pont, Jr. received his formal education at boarding schools, first at St. Paul's School in Concord, New Hampshire, and from 1914 through 1916 at St. Luke's School in Wayne, Pennsylvania. He began his career during World War I as a plant manager for the Ball Grain Explosives Company (his father was on the board of directors). In November 1921, William du Pont, Jr. was elected to the board of directors of the Delaware Trust Company, where his father was president (and chairman of the board from 1923) and a major stockholder. After William du Pont's death in January 1928, his son became the president of Delaware Trust Company in 1929 and was the youngest bank president in Wilmington at that time. In 1952, William du Pont, Jr. became chairman of the board, retaining both positions until his death in 1965. He also sat on the board of directors of E.I. du Pont de Nemours and Company from 1930 and was a member of its Financial Committee (Committee on Audit).

Besides being a prominent local financier, William du Pont, Jr. was well known as a proponent of equestrian arts and sports. His childhood spent at his father's estates provided him with plenty of opportunities to learn about and love horses and hunting dogs. He established his first foxhound pack in 1912 at Montpelier and in 1926 moved it to the farm in Cecil County, Maryland, later known as his Fair Hill estate. The Foxcatcher Hounds pack, named after his farm in Pennsylvania, was well recognized among foxhunting clubs of America. William du Pont, Jr. was an active member of the American Foxhound Club (he held offices of vice president and president), Masters of Foxhound Associations of America, and a number of local foxhunting clubs in Pennsylvania, Maryland, Virginia, and Delaware. He organized and operated the Foxcatcher Hounds Hunting Club at his premises in Fair Hill, Maryland, as a seasonal hunt for his family members and friends.

His love of hunting led William du Pont, Jr. to become an enthusiastic horse rider and owner of Thoroughbred race horses. His horses stabled at Bellevue Hall, Delaware, and Walnut Hall Farm, Virginia, were trained by well-known trainers Preston E. Burch (1884-1978) and Richard E. Handlen (1897-1963) and won important races throughout the nation. William du Pont, Jr. built training race tracks at Bellevue and Fair Hill and instituted the Fair Hill Steeplechase as a benefit for Union Hospital at Elkton, Maryland. Together with his sister Marion du Pont Somerville Scott (1894-1983), he operated the annual Montpelier Horse Show (started by their father in 1906) and Montpelier Hunt Race Meeting, which included flat and steeplechase races.

William du Pont, Jr. was recognized internationally as an authority on the design and construction of horse racing courses. He designed more than twenty-five steeplechase and flat racing tracks, among them Delaware Park (Stanton, Delaware) and the National Cup course at Fair Hill, Maryland, a course equivalent to England's Grand National at Aintree. From 1933 through 1937, he worked with the Delaware Racing Commission and the Delaware Steeplechase and Race Association on state legislation to promote Thoroughbred horse breeding and to establish the race track. His initiative brought pari-mutual racing to Delaware with the opening of Delaware Park on June 26, 1937.

Due to his interest in horses, William du Pont, Jr. sponsored research in equine veterinary medicine, including studies in equine infectious anemia, stallion fertility, equine virus abortion and equine rhinopneumonitis, parasitic diseases, nutritional disorders, and colitis. He was an active member of the Grayson Foundation, an organization committed to the support of scientific investigations into the nature, causes, and development of horse diseases and injuries and methods for preserving and improving the health of horses. From the 1940s through the 1960s, he held the positions of Foundation president and chairman of its Executive Committee. In this capacity, he worked closely with the American Thoroughbred Breeders' Association to obtain and distribute funds to support research at veterinary medicine departments and laboratories of the Universities of Kentucky, Maryland, Pennsylvania, Tennessee, and Cornell and Vanderbilt Universities.

William du Pont, Jr. was the owner of one of the premier herds of the American beef breed, Santa Gertrudis cattle. His herd resulted from a breeding program he designed in the 1940s through 1950s with the help of Robert J. Kleberg Jr. (1853-1932). Kleberg was the owner of the King Ranch, Kingsville, Texas, where the breed was initially developed in the 1920s. After William du Pont, Jr.'s death, his Santa Gertrudis purebred cattle were offered for sale and were purchased entirely by Kings Ranch-a sign of the exceptional quality of the herd.

After equestrian pursuits, du Pont Jr. sports interest was tennis, which he began playing during his school years. He was a member of the Delaware Lawn Tennis Association from the 1930s and its president from 1945 through 1953. In the late 1930s through the 1940s, he was involved with the Southern California Tennis Association. He was acquainted with its secretary, later president, Perry T. Jones (1890-1970), who was known as "Mr. Tennis of the West Coast," and famous female players who successfully represented the United States at international competitions: Althea Louise Brough (1923-2014), Alice Marble (1913-1990), Eleanor Tennant (1895-1974), Doris Jane Hart (1925-2015), Mary Arnold (1916-1975), Katherine Winthrop (1914-1997), Pauline Betz (1919-2011), and Helen H. Jacobs (1908-1997).

One of these tennis players was Margaret Evelyn Osborne (1918-2012), who married William du Pont, Jr. on November 26, 1947. Margaret Osborne was a famous tennis champion and won thirty-seven single and double Grand Slam tournaments. The couple settled in Bellevue Hall, where an outstanding private tennis complex was built. Both Margaret and William du Pont, Jr. contributed extensively to the organization and financed local tennis clubs and school tennis programs in Delaware. Their only child, William du Pont III, was born July 22, 1952. After his birth, Margaret Osborne du Pont returned to professional tennis and won nine doubles championships at Wimbledon and the US Open. William and Margaret du Pont were divorced on March 27, 1964. William du Pont described the situation: "Margaret will be at Reno as she wants a divorce. She hasn't found the reason yet except that I am doing the same things as usual-foxhunting, shooting, and racing. Since she quit playing major tennis, she has taken up squash, table tennis and runs with a different group so our paths seem to have separated." (William du Pont, Jr. to Alice Marble, February 14, 1964, letter to Alice Marble (Business Papers-Point Happy, Inc.-Correspondence).

William du Pont, Jr. died on December 31, 1965, in the Memorial Division of the Delaware Hospital.