I am not sure where all superheroes came from, but I am pretty sure most of them came from the movies. Yeah, maybe Superman was based on some football quarterback from high school who used to give wedgies to the guys who came up with Superman, but the other ones are a lot easier to figure out.
The Incredible Hulk is just a muscular Frankenstein monster. He’s green, he’s got the flat head and everything, at least in the earlier incarnations.
Now, for my new theory: The Mighty Thor. Yes, I was watching TCM, and I saw, for the first time, the silly 1940 movie One Million BC, starring Victor Mature and Carole Landis (It was remade as One Million Years B.C. by Hammer Films in 1966 with Raquel Welch in her fur bikini and dinosaurs by Ray Harryhausen.). And in this movie, at the beginning, a few archaeologists or whoever is with them stumble into some cave during a storm and find some cave paintings. Then the movie goes back in time to recreate, or create from whole cloth, the cave paintings. Now try to tell me that Stan Lee saw that and didn’t say: “What if someone stumbled into a cave and found something else, like Thor’s hammer?” I believe this movie, as silly as it is, is the genesis for Thor, the comic book superhero. I could be wrong, but I doubt it. It doesn't really matter, but where great ideas come from really interests me. I love being able to follow that thought process and see how it happened. I think more people should care about this. Maybe it should be a new science.