|I am Providence.|
Today, his form of "Yog-Sotherey" -- what we today call the Cthulhu Mythos -- has become a prevalent form of horror for books, movies, games, even plush Cthulhus and other toys. It's a well-known fan meme. Ken Hite has suggested that all of this absorption into fan culture proves that Cthulhu and his otherworldly ilk are iconic figures, like Superman.
What is Lovecraft's lasting legacy? Others on the 'net have expressed this in a more erudite form than I could. I believe it is not only his own brand of "cosmic horror", the idea that there are things in the universe so completely strange and alien to us that our fragile minds cannot fathom them, not only the idea that humans are as insignificant to them as an insect might be to us, but the true message is that human beings are fully capable of reaching those same heights of inhumanity. I often wonder what H.P. would have thought had he lived to see the scale of atrocities during the 20th century.