George III was the King of the United Kingdom from 1760 to 1820.
In 1762, Lolita trapped George III in a natural-time envelope so that she could use him as a puppet in her attempted invasion of Britain. (AUDIO: In the Year of the Cat)
In 1774, George received the last mammoth in Europe as a gift from Catherine II of Russia. (COMIC: Political Animals, PROSE: Grass, The Adventuress of Henrietta Street) In December of that year it was to have been part of the Royal hunt. This mammoth was vital to the last surviving members of Faction Paradox and other interested parties. It was thought a relic which would act as a focal point around which history could be shaped. The ritual of the hunt itself was to determine who would control the future. The focus of the hunt, however shifted to the last of the Mayakai. (COMIC: Political Animals, Bêtes Noires & Dark Horses)
The Doctor met George III prior to 1814. (AUDIO: Washington Burns)
His Chancellor of the Exchequer was Sir Francis Dashwood. (AUDIO: Minuet in Hell)
Behind the scenes
He was played by Gertan Klauber in Blackadder the Third, David Warner in The American Revolution and Nicholas Rowe in Longitude.