"Crusty" Trussett is a wizard referenced in The Last Continent. When a temporal accident ages Ponder Stibbons to well over eighty, Stibbons starts thinking and acting like an elderly wizard and reminiscences about the sort of things old Crusty got up to in the old days. Then he remembers Trussett is his own age and would still only be about twenty-four. The temporal confusion this causes gives Ponder the key to return to his own early-twenties self. By inference Trussett would be a peer who graduated with Ponder at the same time and who may be one of the many younger wizards in the High Energy Magic Building.