That's the question Geoff Boucher is asking over at Hero Complex, based on a 1915 cover to Collier's magazine he bought for $10.

"I remember being a bit startled when I saw the image for the simple fact that it was a comic book-style hero more than two decades before Superman and Batman," he writes. He notes the character came before The Shadow and Zorro, but not the Scarlet Pimpernel, who debuted on stage in England in 1903.

As to who the Gray Mask is and who wrote the story, writer Christopher Farnsworth responds in the comments section with some additional information. The story in Collier's was written by Charles Wadsworth Camp, father of author Madeleine L'Engle. The full prose story can be found on Google books. And there was a silent film made out of the story as well.