As mentioned before, the Heap was the first of the comic book swamp monsters. As Don Markstein puts it:
The Heap was comics' very first shambling muck monster, tho he was undoubtedly inspired by Theodore Sturgeon's 1940 short story, "It", the template for all shambling muck monsters to come. "It" told of a man who died in a swamp, fermented in a broth of rotting vegetation, and eventually rose again, half man, half fetid vegetable matter, to wreak vengeance upon his foes. Another prominent "It"-inspired comic book character of the 1940s was DC's Solomon Grundy, who bedeviled Green Lantern starting in 1944.I have no idea how our shambling hero made it to the American Southwest, but if questions like that bother you then you shouldn't be reading comic book in the first place.
In The Heap's case, the man in the muck was Baron von Emmelmann, who had everything to live for — wealth, social position, loving wife, baby he hadn't yet seen, etc. — when, on October 12, 1918, his plane was shot down over Poland's Wausau Swamp. Lying lifeless as his body slowly merged with the morass, he had nothing left but his will to live, to rise, to return to the world of humans.