3 March 1863 - 15 December 1947
A Welsh writer who spent much of his adult life in London, Machen devoted many of his supernaturalist works to an exploration of a mythic vein of the post-Gothic. His works have frequent recourse to the idea that some vestige of a primitive, malefic, pre-Christian "Little People" has survived into the present, and Machen explores the metaphysical implications of this possibility with gusto. Largely eschewing the mid- to late-Victorian interest in the psychological implications of the supernatural, Machen set the stage for the Cthulhu horrors of Lovecraft and others at the same time that his work testifies to the demise of Victorian complacency and self-assurance.
"The Great God Pan"
The work that shocked Victorian England when it was first published in 1890 (in the short-lived magazine Whirlwind; first book publication was 1894), it cemented in the public mind the association of Machen with the Decadence movement of Wilde et al. But the significance of this work is much larger, for it most famously articulates the mythic power that Machen so frequently sought for his work.
"The White People" 
In the opinion of a number of critics, including yours truly, this is Machen's best work, a powerful and disturbing tale of the Celtic and primal "Little People" mentioned above.
"The Bowmen" [29 September 1914] (19K)
Machen's famous tale about the ghostly intervention of the archers of Agincourt on a WWI battlefield; the tale (which includes a wonderfully weird vegetarian angle) took on a life of its own, with many people claiming to have actually seen the ghostly soldiers. Machen's repeated claims that the work was pure fiction did little to deter the popular sentiment that benevolent supernatural forces did indeed intervene on behalf of English soldiers. For more on this "Angels of Mons" (the town where the battle was fought) controversy, click here. [Aftermath: When the Boys Came Home]
Machen also discusses his writing of the tale, and the public reception of it, in this introductory note. [Gaslight]
Machen's Introduction to The Three Imposters [R. T. Gault]
A passage from Machen's autobiography (the second volume)
in which Machen discusses some of the strange, quasi-hallucinatory experiences during his time in London and his involvement in the Order of the Golden Dawn [R. T. Gault]
On the Kabbalah
An extract from the 2nd volume of Machen's autobiography in which he discusses the Kabbalah and other strange, mystical things [R. T. Gault]