William Cavendish, 4th Duke of Devonshire,, styled Lord Cavendish before 1729, and Marquess of Hartington between 1729 and 1755, was a British Whig statesman and nobleman who was briefly nominal Prime Minister of Great Britain. He was the first son of William Cavendish, 3rd Duke of Devonshire and his wife, Catherine Hoskins. He is also a great-great-great-great-great-grandfather of King Charles III through the king's maternal great-grandmother.

William Cavendish, 3rd Duke of Devonshire, was a British nobleman and Whig politician who sat in the House of Commons from 1721 to 1729 when he inherited the Dukedom.