William Cavendish, 5th Duke of Devonshire,, was a British nobleman, aristocrat, and politician. He was the eldest son of William Cavendish, 4th Duke of Devonshire, by his wife, the heiress Lady Charlotte Boyle, suo jure Baroness Clifford, who brought in considerable money and estates to the Cavendish family. He was invited to join the Cabinet on three occasions, but declined each offer. He was Lord High Treasurer of Ireland and Governor of Cork, and Lord Lieutenant of Derbyshire. In 1782, he was made a Knight of the Order of the Garter.

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.