Georgiana, the Duchess of Devonshire, is a particularly interesting character from late 18th and early 19th Century British history. She was the daughter of the first Earl of Spencer (which makes her one of the ancestors of Diana, the Princess of Wales) and the wife of William Cavendish, the fifth Duke of Devonshire. Both her father and her husband were scions of the Whig party, and Georgiana was an important personage in the Whig party in her own right. She was a relentless campaigner for Whig candidates (particularly Charles Fox), and and it was largely her skill and determination that kept the Whigs together through the dark times during Pitt's ascendancy in the 1780s and 1790s. More than that, she was also the arbiter of fashion and the very center of fashionable aristocratic society. In other words, she might not have ranked in importance quite at the same level as William Pitt the younger, the great Prime Minister, but she's not that far behind.
Georgiana has been the subject of a number of biographies, the most recent of which was Amanda Foreman's Georgiana: Duchess of Devonshire, which is a pretty good read and a decent piece of scholarship (although I think that Foreman identifies a bit too closely with Georgiana). Well, period movie fans, Foreman's book is being made into a movie!
It will be interesting to see what Hollywood makes of the story. Georgiana was a prominent figure on the British scene from the time of her marriage at age 17 until her death at age 49, and it looks from the cast list that the movie aspires to cover most of her life. That's unfortunate since it seems likely that it will cover none of it very well; but I will be looking forward to it anyway. Who knows? Georgiana's affair with Edward Grey (later Earl Grey, the guy that the type of tea is named after) might make for some good bodice-ripping action.