He went to Mars through some kind of mysterious process that was never fully explained. Something like transmigration of the soul and re-embodiment, as far as I recall. He found himself standing naked and unarmed on the Red Planet, and had to deal with the situation. Luckily he had the natural fighting skills of Sir Lancelot, Richard the Lionheart, and Wyatt Earp, and immediately took charge of the situation, despite being attacked by 8-limbed greenskinned Thark warriors and vicious 8-limbed Martian beasts. Pretty good for a guy from Virginia, eh?