Angier Biddle Duke was an American diplomat who served as Chief of Protocol of the United States in the 1960s. Prior to that, at the age of 36, he became the youngest American ambassador in history when he was appointed to be the U.S. Ambassador to El Salvador.

The Biddle family of Philadelphia, Pennsylvania is an Old Philadelphian family descended from English immigrants William Biddle (1630–1712) and Sarah Kempe (1634–1709), who arrived in the Province of New Jersey in 1681. Quakers, they had emigrated from England in part to escape religious persecution. Having acquired extensive rights to more than 43,000 acres (170 km2) of lands in West Jersey, they settled first at Burlington, a city which developed along the east side of the Delaware River.