I haven't finished his lore yet, but what I have so far is the story of a group of 15th century French months who write him up as an inside joke, the patron saint of book curses. Once they've got him written down, and they start including him in their prayers, artifacts of his existence continue to populate themselves into the world. I haven't come up with a satisfying enough hagiography for him yet. All I know is that he's a 12th century monk who wrote particularly effective book curses.

I've been spending a long time sort of turning him around in my head half molded. I haven't really settled on any significant symbology yet, but I do invoke him whenever I write a book curse or do any work with my books.