Sarah Churchill, Duchess of Marlborough (née Jenyns, spelt Jennings in most modern references; 5 June 1660 (Old Style) – 18 October 1744) rose to be one of the most influential women of her time through her close friendship with Queen Anne of Great Britain. Sarah's friendship and influence with Princess Anne was widely known, and leading public figures often turned their attentions to her in the hope that she would influence Anne to comply with requests. As a result, 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, John Churchill, 1st Duke of Marlborough. She acted as Anne's agent after Anne's father, James II, was deposed during the Glorious Revolution; and she promoted her interests during the rule of James's successors, 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, the first Earl of Godolphin, rose to head the government, partly owing to his wife's friendship with the Queen. While the Duke was out of the country commanding troops in the War of the Spanish Succession, Sarah kept him informed of court intrigue, while he sent her requests and political advice, which she would then convey to the Queen. Sarah tirelessly campaigned on behalf of the Whigs, while also devoting much of her time to building projects such as Blenheim Palace.
Sarah, a strong-willed woman who liked to get her own way, tried the Queen's patience whenever she disagreed with her on political, court or church appointments. After her final break with Anne in 1711, Sarah and her husband were dismissed from the court, but she had her revenge under the Hanoverians following Anne's death. She had famous subsequent disagreements with many important people, including her daughter the second 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 at the age of eighty-four. SOURCE: Wikipedia