Little is known about this denizen of Paris; it is a fairly long time after his introduction before the reader even learns his name. (This wiki went with "Monsieur Andouille" in the interim.). He first appears in the comic well-advanced in his plot to overthrow the Master of Paris in (he thinks) collaboration with remote clank-puppeteer Drusus Beausoleil, who is revealed to actually be an official covert agent for the Master.
Du Quay's plan is thus: he has connected a salvaged piece of Castle Heterodyne (complete with a copy of the Castle's intellect) to a Telluric Wave Conductor and has ordered the resulting gestalt to subvert and take over all the thinking machines of Paris. After being dragged into Du Quay's lair, Agatha is allowed by her kidnapper Beausoleil to tinker with this system as a test of her abilities. This gives her control of said system (and evidently all of Paris) when the Castle-copy accepts her as The Heterodyne.
Discovering this, Du Quay takes a shot at Agatha with his Death Ray, but Der Kestle hijacks the current Drusus clank to shield her from the blast. When the Castle patronizingly rejects his attempt at re-establishing control, Du Quay ascends to full level 3 laughing madness and activates a self-destruct mechanism that in theory will not only blow up his lair, but all of Paris. He is quickly subdued by Agatha by means of a wrench to the head, and the Castle casually deactivates the self-destruct. The Master then appears on the scene in person, equally casually cuts off Der Kestle's control, and prepares to arrest both Du Quay and Agatha.
Du quay in French means of, by or from the docks. So this Du Quay's family might have been shipwrights or dockworkers at one time.