I picked up Gladiator because I heard it was an inspiration for Doc Savage and Superman. That is an understandment.
Gladiator is the story of Hugo Danner. Hugo is the son of a scientist who injected him with a serum when he was still in the womb, giving him unbelievable strength. For example, Hugo kills a bully at school with his superhuman strength, branding him an outsider for the rest of his life.
Over the course of the book, Hugo goes from relationship to relationship, works in a circus, fights in a war, all the while looking for a place to belong. Hugo being an outsider reminded me a lot of the way The Hulk and the X-Men are treated. In fact, Hugo's story seems like the template for a lot of later superhero characters.
I'd recommend this to any comic book or Doc Savage fan interested in looking at the ancestor of their heroes.