The Lexicon: An Unauthorized Guide to Harry Potter Fiction and Related Materials is a book written by Steve Vander Ark. The book has information and details about everything going on in the universe in which Harry Potter, Ronald Weasley, Hermione Granger, Draco Malfoy, Vincent Crabbe, Gregory Goyle, Pansy Parkinson, Albus Dumbledore, Severus Snape, Tom Riddle/Lord Voldemort, Dudley Dursley and many other characters lives.