Sarah Churchill, Duchess of Marlborough

Sarah Churchill, Duchess of Marlborough (née Jenyns, spelt Jennings in most modern references; 5 June 1660 (Old Style) – 18 October 1744), was an English courtier who became one of the most influential women of her time through her close relationship with Anne, Queen of Great Britain. Churchill's influence on Anne was widely known, and leading public figures often turned their attentions to her, hoping to attain favour from the queen.

Churchill enjoyed a "long and devoted" relationship with her husband of more than 40 years, the general John Churchill, 1st Duke of Marlborough. After Anne's father, King James II, was deposed during the Glorious Revolution, Churchill acted as Anne's agent, promoting her interests during the reigns of William III and Mary II. When Anne came into power after William's death in 1702, John Churchill and Sidney Godolphin, 1st Earl of Godolphin, rose to head the government, partly owing to the Duchess.

While John Churchill was fighting in the War of the Spanish Succession, the Duchess kept him informed of court intrigues and conveyed his requests and political advice to the Queen. The Duchess campaigned tirelessly on behalf of the Whigs, while also devoting herself to building projects such as Blenheim Palace. However, her political ambitions strained her relationship with the Queen; their relationship ended in 1711, and the Duke and Duchess were dismissed from court. Later, Churchill had famous disagreements with many important people, including her daughter Henrietta Godolphin, 2nd Duchess of Marlborough; the architect of Blenheim Palace, John Vanbrugh; Prime Minister Robert Walpole; King George II; and his wife, Queen Caroline. The money she inherited from the Marlborough trust left her one of the richest women in Europe, and she possessed 27 estates at the time of her death. She died in 1744, aged 84, and was buried at Blenheim.