Who is Lubbert Das?

I understand that Lubbert Das is the name of the character depicted in Bosch's famous Extraction of the Stone of Madness, but I've read that Lubbert is a common name for a dunce that appears in Dutch literature. That's all that I can find. What Dutch literature? What kind of dunce? Like a Mulla Nasruddin kind of character, or just a dope? If someone could actually point me towards a piece of literature in which a Lubbert appears I would be greatful.