Writers that Gaiman mentioned as significant influences include C. S. Lewis, J. R. R. Tolkien, Lewis Carroll, Mary Shelley, Rudyard Kipling, Edgar Allan Poe, Michael Moorcock, Dave Sim, Alan Moore, Steve Ditko, Will Eisner, Ursula K. Le Guin, Harlan Ellison, Lord Dunsany and G. K. Chesterton. A lifetime fan of the Monty Python comedy troupe, as a teenager he owned a copy of "Monty Python's Big Red Book". When he was 19–20 years old, he contacted his favourite science fiction writer, R. A. Lafferty, whom he discovered when he was nine, and asked for advice on becoming an author along with a Lafferty pastiche he had written. The writer sent Gaiman an encouraging and informative letter back, along with literary advice.