The Librarian considered matters for a while. So...a dwarf and a troll. He preferred both species to humans. For one thing, neither of them were great readers. The Librarian was, of course, very much in favor of reading in general, but readers in particular got on his nerves. There was something, well, sacrilegious about the way they kept taking books off the shelves and wearing out the words by reading them. He liked people who loved and respected books, and the best way to do that, in the Librarian's opinion, was to leave them on the shelves where Nature intended them to be.