William the Conqueror
From Jenny Everywhere Wiki
According to Sylvester Shoebill, “few people [were] up to snuff on their William the Conqueror economics,” for which reason few understood the historical allusion in the name of the Council of Frogs' Doomsday Book. (PROSE: The Grand Multiverse Hotel)
Behind the scenes
By virtue of being a real historical figure, William the Conqueror can be considered a public-domain character in his own right.