Mr Winvoe is a very seriously minded Assassin, who looks after the financial administration of the Assassins' Guild. The Guild Treasurer is therefore a man of great responsibilities and carries a great weight upon his shoulders. He is a member of the Dark Council by default and is encountered in Hogfather. His brief appearance suggests that he has a lot in common, professionally and personally, with the Bursar at Unseen University, although in Lord Downey he has has a far more understanding superior who has not yet driven him in the direction of the Dried Frog Pills.
Interestingly, on Esoteric Street, there is a firm of accountants called Winvoe and Prood. (At the sign of the Crossed Quills). Possibly a related Winvoe?