Sir George was one of the nobles of Ankh-Morpork called to hear Edward d'Eath rant about kings during Men at Arms. While he didn't actually speak, presumably he agreed with the other nobles: the city works, and therefore we should not mess around with it, even though we have virtually no power anymore, and the city is ruled by ragtags of traders and merchants, and a tyrannical, unpleasant, jumped-up little man. Evidently, he disagreed with Edward's assertion that the time of the Kings of Ankh was a golden age.
In Hogfather, Teatime is mentioned as having been given a contract to inhume Sir George. Specifically, the unnamed client wanted Teatime to check his breathing with a mirror. To the annoyance of Lord Downey, while Teatime indeed checked Sir George's breathing with his mirror, the man's head was several feet from his neck at this point. And Teatime saw absolutely nothing incongruous about this. And of course, since he couldn't have the servants (an old man and a maidservant) bursting in, he killed them as well. After this inhumation, the Guild Council agreed to dismiss Teatime (in the same way pupils of the Assassins' Guild are Failed), but Downey decided not to, as Teatime's special skills were needed for a most unusual target...
What Sir George did to warrant a contract is unknown, as nothing else is known about him apart from the two mentions in the two books above.