I saw John Carter of Mars last night with my two sons. First off, I have to say that is was a really, really great movie.
It got me thinking though about John Carter's place in Metahuman history. When I think of the first "superhero", I immediately think Superman, but I know many credit the book "Gladiator" as containing the first "superhero" even though the main character never fought crime, he was bulletproof and exceptionally fast and strong. He seems a close approximation of "Golden Boy" from the "Wild Cards" series (though the character in Gladiator has a different origin - all metahumans in the "Wild Cards" series have a shared origin through an alien virus).
In any event, I immediately went to the interwebs to solve this conundrum and came upon a relatively decent argument that Mandrake the Magician could be considered the first superhero with his ability to mesmerize people and the fact that he fought baddies.
Through the comments on the Mandrake argument, however, I found people confused by the argument. People asked, "What about Jesus? The Greek Gods? Robin Hood? Zorro?"
So for the sake of the argument, I would say Robin Hood, Zorro, Tarzan don't count. They don't have "powers". Some folks from these old stories do though (Merlin, Gawain). But I would lump Merlin in with the Greek Gods as mythology and/or religion. Jesus falls in one of those two categories (depending on your belief system). So we are left with the following definition - Metahuman powers, not of mythological or religious origins and probably created in America.
That being the case, I would say that superheroes are an invention of the 20th century, but rather than Superman, Mandrake or the dude from Gladiator, probably began with John Carter. Same origin as Superman (sent to an alien planet - Mars in this case - and give metahuman powers due to the planet's environment. He then uses those powers to fight oppression).
So, to summarize this very long and rambling post - Go see John Carter of Mars, a movie about the FIRST Superhero.