A Possible Source

I've looked, but have never been able to find any info on the source or inspiration for Alex Toth's strange characters.

A possible source might be discovered among the ferment of weird fiction from the pen of Manly Wade Wellman, whose stories were published by Arkham House.
http://en.wikipedia.org/wiki/Manly_Wade_Wellman

When I was a child, I encountered one of his tales, The Desrick on Yandro, anthologized in Alfred Hitchcock's Monster Museum. The tale features a number of peculiar creatures, like the Bammat, the Toller, the Flat (whose amorphous shape suggests Gleep & Gloop), the Behinder, and the Culverin, who shoots pebbles (like Tundro). There was something about the monsters from this story which reminded me of the Herculoids, though nothing else would suggest the characters or storylines. Other aspects of the Herculoids remind me of the weird fiction of Robert E Howard, best known as the creator of Conan the Barbarian.
http://www.conan.com/

§« El sueño de la razón produce monstruos. »§