Sarah Churchill, Duchess of Marlborough (d. 1744)
Sarah Churchill, Duchess of Marlborough, Princess of Mindelheim, Countess of Nellenburg (née Jenyns, spelled Jennings in most modern references; 5 June 1660 (Old Style) – 18 October 1744), was an English courtier who rose to be one of the most influential women of her time through her close relationship with Anne, Queen of Great Britain. Sarah's relationship and influence with Princess Anne were widely known, and leading public figures often turned their attentions to her, hoping for favor from Anne. By the time Anne became queen, Sarah’s knowledge of government and intimacy with the queen had made her a powerful friend and a dangerous enemy.

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

While the Duke was fighting the War of the Spanish Succession, Sarah kept him informed of court intrigue and conveyed his requests and political advice to the queen. Sarah campaigned tirelessly on behalf of the Whigs, while also devoting herself to building projects such as Blenheim Palace. A strong-willed woman, she strained her relationship with the Queen whenever they disagreed on political, court, or church appointments. After her final break with Anne in 1711, Sarah and her husband were dismissed from Court, but she had her revenge under the Hanoverian kings following Anne's death. She later 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. She died in 1744, aged 84.