A Princess of Mars

A Princess of Mars is a science fantasy novel by Edgar Rice Burroughs, the first of his Barsoom series. John Carter, a Confederate veteran of the American Civil War, goes prospecting in Arizona immediately after the war's end. Having struck a rich vein of gold, he runs afoul of the Apaches. While attempting to evade pursuit by hiding in a sacred cave, he is mysteriously transported to Mars, called "Barsoom" by its inhabitants.
Carter finds that he has great strength and superhuman agility in this new environment as a result of its lesser gravity and lower atmospheric pressure. He soon falls in with a nomadic tribe of Green Martians, or Tharks, as the planet's warlike, six-limbed, green-skinned inhabitants are known. Thanks to his strength and martial prowess, Carter rises to a high position in the tribe and earns the respect and eventually the friendship of Tars Tarkas, one of the Thark chiefs.