Machen is another one of those authors who was extremely influential on Lovecraft. He is best known for his weird fiction, and last weekend I read his book The Three Impostors, published in 1895. Lovecraft had some mixed feelings about this book, calling it "a work whose merit as a whole is somewhat marred by an imitation of the jaunty [Robert Louis] Stevenson manner." Stevenson's book New Arabian Nights was apparently a model for Machen.
However, Lovecraft also said that this book contains "certain tales which perhaps represent the high-water mark of Machen's skill as a terror-weaver."