Archchancellor Weatherwax was in charge of UU in the time of The Light Fantastic, estimated (by some deeply contorted calculation) to be set about 25 years before the time of Hogfather.
In Lords and Ladies, Terry supplies the following piece of dialogue (on p. 224/161) between Granny and Archchancellor Ridcully as an answer:
“‘There was even a Weatherwax as Archchancellor, years ago,’ said Ridcully. ‘So I understand. Distant cousin. Never knew him,’ said Granny.”