Harriet Rebecca Lane Johnston acted as first lady of the United States during the administration of her uncle, lifelong bachelor President James Buchanan, from 1857 to 1861. She has been described as the first of the modern First Ladies, being a notably charming and diplomatic hostess, whose dress-styles were copied, and who promoted deserving causes. In her will, she left funds for a new school on the grounds of Washington National Cathedral. Several ships have been named in her honor, including the cutter USCGC Harriet Lane, still in service.

First Lady of the United States (FLOTUS) is the title held by the hostess of the White House, usually the wife of the president of the United States, concurrent with the president's term in office. Although the first lady's role has never been codified or officially defined, she figures prominently in the political and social life of the United States. Since the early 20th century, the first lady has been assisted by official staff, known as the Office of the First Lady and headquartered in the East Wing of the White House.