John Carter? Of Mars? The dude is pretty much the superman of that setting because he is a human from planet earth.

Tolkien needs to be mentioned again. Humans (or Men) are special in that setting, even if you are confused by the so-called apparent elven superiority.

3.5 D&D and Pathfinder subvert this by playing it straight. Humans are special because they are "the mario". Most of the time, humans are the most powerful race, both within the game and in metagame. Humans have more drive, diversity and resourcefulness than other races to reach the stars. Metagame is even more brutal. That extra Feat and Skill Point per level (and +2 to Stat of choice in Pathfinder) really do make the difference.

In Warhammer 40000 the imperium of man has conquered the galaxy because no other race is as warlike. Even the forces of Chaos (Bad Guys) pale in comparison to the extent and volume of atrocities the imperium has commited. I'm pretty sure that if imperium went suddenly totally pacifist forces of Chaos would collapse because they are fueled by the negative aspects of living beings. I mean, c'mon, the imperium has killed more of its citizens than Chaos ever has. Really:

"For more than a hundred centuries the Emperor has sat unmoving on the Golden Throne of Earth. He is the master of mankind by the will of the gods and master of a million worlds by the might of his inexhaustible armies. He is a rotting carcass writhing invisibly with power from the Dark Age of Technology. He is the Carrion Lord of the Imperium for whom a thousand souls die every day, for whom blood is drunk and flesh eaten. Human blood and human flesh - the stuff of which the Imperium is made. (...) Forget the power of technology, science and common humanity. Forget the promise of progress and understanding, for there is no peace amongst the stars, only an eternity of carnage and slaughter and the laughter of thirsting gods."