William Henry Cavendish Cavendish-Bentinck, 3rd Duke of Portland (14 April 1738 – 30 October 1809) was a British Whig and 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 (1807–09). The twenty-four 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 is also a great-great-great-grandfather of Elizabeth II through her maternal grandmother.