Henry the Taupé
Henry the Taupé is referenced in the Discworld Thieves' Guild Yearbook and Diary 2002 as an interesting example of Demarcation in action. Professor of Criminology at Unseen University, his professional area of expertise necessarily overlapped that of the Thieves' Guild, and this was informally accepted by all sides. Henry lost all faith in human nature after setting up a practical experiment in confidence trickery where he wanted to see what people would do even if they knew, and had clearly been told in advance, that they were being cheated in a rigged game. He set up a Find-The-Lady table in Sator Square and clearly and repeatedly announced to a gathering crowd hungry for street theatre that they would not win, that the game was rigged, and the only person who would walk away with any money would be him. To his consternation, people played anyway and Henry ended the afternoon $AM200 better off. Even though this is only restating a perfectly obvious quirk of human nature well known to people of a Moist von Lipwig inclination, being able to professionally state this in academic terms made Henry's name. Even though he was disillusioned ever after concerning human nature and general stupidity. His work in criminology is respected by the more intellectual Thieves, and he has the status of a Visiting Lecturer at the Thieves' Guild School.
His wizard name is probably because in a profession where wizards tend to name themselves according to the formula (Name) + the (Colour), there really aren't all that many colour terms to go round, and the more popular and obvious ones tend to get used first.