The Librarian is the propriator of a mobile library, which resembles a full sized library with lion statues on the front and everything, but miniature, and with only a window through which the Librarian hands out or receives books.
In Wrath of the Librarian, Courage finds that he has a 2 years passed due library book. Taking it to the mobile library, the Librarian refuses to accept it back until he pays the overdue fee, which by now is several hundred dollars in value. Courage has no money, and so leaves to find some. the librarian in the meanwhile, curses the book that he possesses, which later causes Muriel and Eustace to mutate into the two title characters of the book.
As Courage tries to stop the two of them causing mayhem in town, the return fee continues to increase. Courage tries to appeal to the Librarian, but she denies him, pointing out the ever growing return charge. Eventually, Courage uses Muriel and Eustace, who have taken their fairyland antics to a zoo, as a show in order to charge money from a gathering crowd. taking up 10,000 dollars, the then price fo the overdue fee, Courage attempts to pay off the book, only to find he is one pence under. He pulls a penny from his foot, and tosses it on. The Librarian stamps the book, and ends the curse, causing Muriel and Eustace to revert back to normal.
As the crowd cheer the happy ending, the Librarian pokes her head out of a snake's mouth, and shushes them.
The Librarian never speaks, but does frequently tell people, mostly Courage, "Shh!"