 "The Art of Discworld" confirms that the Librarian was indeed Dr. Horace Worblehat, and that his fears of turning back into human are baseless at most.Rincewind is apparently the only wizard who still remembers the Librarian's name, but he has agreed not to tell anyone, possibly because the Librarian is capable of bouncing the head of a man on the pavement when holding him by the ankle.The Librarian served a brief stint in the City Watch during the reign of terror caused by the dragon of Ankh-Morpork, where he helped to rescue Sam Vimes from the Patrician's cell.