Georgiana, Duchess of Devonshire (June 7, 1757 - March 30, 1806), born Lady Georgiana Spencer, was the first wife of William Cavendish, 5th Duke of Devonshire and mother of William George Spencer Cavendish, 6th Duke of Devonshire. Her father, John, 1st Earl Spencer, was a great-grandson of John Churchill, 1st Duke of Marlborough. Her niece was Lady Caroline Lamb. Among her descendants are the present Duke of Devonshire (via her granddaughter).
Georgiana was a celebrated beauty and a socialite who gathered around her a large circle of literary and political figures -- a salon. She was also an active political campaigner in an age when women's suffrage was still over a century away. Both the Spencers and the Cavendishes were Whigs. Georgiana campaigned for the Whigs -- particularly for a distant cousin, Charles James Fox -- at a time when the King (George III) and his Ministers had more direct influence over the House of Commons, principally through their power of patronage. During the 1784 general election, the Duchess was rumored to have traded kisses for votes in favor of Fox.
Georgiana married the future Duke on June 6, 1774. The marriage was a brilliant but unhappy one, with the couple mismatched by temperament. The young Duchess's early childlessness was also a matter of concern when aristocratic wives were valued as much for their fertility as for their dowries and connections. She gave birth to two daughters, before the much-awaited heir (and only) son was born. This son William George Spencer Cavendish, 6th Duke of Devonshire died unmarried in 1858; her daughters became Countess of Carlisle and Countess Granville (married to a former lover of her maternal aunt Lady Bessborough).
It was Georgiana who introduced the Duke to his mistress and second wife-to-be, Lady Elizabeth Foster. "Bess" was Georgiana's best friend, and she tolerated the menage-a-trois for many years. Georgiana herself formed a relationship with Charles Grey, 2nd Earl Grey, by whom she had a daughter (an ancestor of Sarah, Duchess of York). Lady Elizabeth Foster had two children by the Duke -- a son and daughter. When the Duchess died, her husband married Bess Foster -- and promptly set up a new mistress. At his death, his son by his first wife Georgiana became 6th Duke but died unmarried. [He was succeeded by a first cousin once removed William Cavendish, 7th Duke of Devonshire (1808-1891), who was widower of the 6th Duke's niece and Georgiana's granddaughter Lady Blanche Howard].
Georgiana was famous not only for her marital arrangements, her beauty and sense of style, her political campaigning, but also for her love of gambling. She was reported to have died deeply in debt, even though her own family the Spencers and her husband's family the Cavendishes were immensely wealthy.
During her years in the public eye, Georgiana was painted by Thomas Gainsborough and Joshua Reynolds. Gainsborough's famous painting of her in a large French hat was lost for many years.
Other well-known women from the same family as Georgiana include Lady Caroline Lamb and Diana, Princess of Wales. Georgiana's brother the 2nd Earl Spencer was ancestor of Diana, Princess of Wales (former wife of Charles, Prince of Wales), who was born Lady Diana Spencer.