William Cavendish-Bentinck, 3rd Duke of Portland, English politician, Prime Minister of the United Kingdom (d. 1809)
William Henry Cavendish Cavendish-Bentinck, 3rd Duke of Portland, (14 April 1738 – 30 October 1809) was a British Whig and then a Tory politician during the late Georgian era. He served as Chancellor of the University of Oxford (1792–1809) and twice as the Prime Minister of Great Britain (1783) and then of the United Kingdom (1807–1809). The 24 years between his two terms as Prime Minister is the longest gap between terms of office of any British Prime Minister.

Portland was known before 1762 by the courtesy title Marquess of Titchfield. He held a title of every degree of British nobility: duke, marquess, earl, viscount and baron. He was the leader of the Portland Whigs faction, which broke with the Whig leadership of Charles James Fox and joined with William Pitt the Younger in the wake of the French Revolution.