William George Spencer Cavendish, 6th Duke of Devonshire KG, PC (21 May 1790 – 18 January 1858), styled Marquess of Hartington until 1811, was a British peer, courtier, nobleman, and Whig politician. Known as the "Bachelor Duke", he was Lord Chamberlain of the Household between 1827 and 1828 and again between 1830 and 1834. The Cavendish banana is named after him.
Born in Paris, France, Devonshire was the son of William Cavendish, 5th Duke of Devonshire, and Lady Georgiana, daughter of John Spencer, 1st Earl Spencer. He was educated at Harrow and at Trinity College, Cambridge. He lost both his parents while still in his youth; his mother died in 1806 and his father in 1811 when, aged 21, he succeeded to the dukedom. Along with the title, he inherited eight stately homes and some 200,000 acres (809 km² or 80,900 ha) of land.
Politically Devonshire followed in the Whig family tradition. He supported Catholic emancipation, the abolition of slavery and reduced factory working hours. He held office as Lord Chamberlain of the Household under George Canning and Lord Goderich between 1827 and 1828 and under Lord Grey and Lord Melbourne between 1830 and 1834. In 1827 he was sworn of the Privy Council and made a Knight of the Garter. He was appointed Ambassador Extraordinary to the Russian Empire on the coronation of Czar Nicholas I in 1826.