The Horla is a supernatural/horror short story by Guy de Maupassassant. Horror author H.P. Lovecraft said this of it: "this tense narrative is perhaps without peer in its particular department", and it's considered an influence on Lovecraft's Cthulhu stories.
You can read it here, or you can have it read to you:
The story was written in 1887. About 4 years later the author was committed to a private asylum after a suicide attempt. He died there the following year at age 42.