Duke Thorburn was a member of the City's aristocracy. Lenny was a former guard of his. The fat duke had a thing for stuffed bears. Duke Thorburn is at the House of Blossoms, he kept talking about his cousin in the treasury. There were plans to blackmail and milk him dry. His boring friend Horatio can also be found at the brothel.
In Thief II, a Lord Thorburn was a member of the upper class who was trying to gain favor with the Mechanists.