William Cavendish, 4th Duke of Devonshire, English politician, Prime Minister of the United Kingdom (born 1720)

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.

The prime minister of the United Kingdom is the head of government of the United Kingdom. The prime minister advises the sovereign on the exercise of much of the royal prerogative, chairs the Cabinet, and selects its ministers. Modern prime ministers hold office by virtue of their ability to command the confidence of the House of Commons, so they are invariably members of Parliament.

October 2 is the 275th day of the year in the Gregorian calendar; 90 days remain until the end of the year.