For the uninitiated:
John Carter first appeared in Edgar Rice Burrough's
A Princess of Mars in 1911. Superman first appeared in 1938. Similarities between the two characters are striking: John Carter, a visitor from another planet (Earth), has (because of the gravity difference between the two planets) incredible strength on his adopted planet, and is, among other things, able to leap great distances in a single bound. He is described as being very muscular (much more muscular than his earthly alter-ego), and stands about 6'2" with close cropped black hair and steel-grey eyes. He is also described as being the very embodiment of old-fashioned, even quaint, values. As shown in >
this< 1919 first-edition book cover, he was even portrayed with a red cape and a curl in the middle of his forehead!
Superman's creators, Jerry Siegel and Joe Shuster,
don't mention John Carter as an inspiration for their iconic super hero, but to my mind the evidence is clear: Carter was the prototype, and as such, could arguably be called the 'father' of all modern superheroes.
As of this writing, Disney/Pixar has just finished location filming for an upcoming live-action John Carter of Mars movie, currently scheduled for release in 2012.
Postscript: Siegel and Shuster can't even claim the skin-tight costume as their idea: in 1936, two years before Superman first appeared, Lee Falk's
The Phantom began running as a daily comic strip with its title character being the first hero to wear a skin-tight outfit. Falk claimed to have gotten the idea from movie depictions of Robin Hood. Falk also gave a nod to another Burroughs character, Tarzan as inspiration. Good for him.