The characters and scenery were all taken from the John Carter series of books by Edgar Rice Burroughs, who created Tarzan as well.
The stories follow the adventures of John Carter of Virginia, an ex-Confederate officer who had found himself transported (magically, although this is never really addressed) to the planet Mars (called by its natives Barsoom). The Burroughs Mars was a place full of red-skinned humans who hatch from eggs, but also larger, four-armed, militaristic Martians who constantly wage war on the humans. Carter of course found himself thrust into the midst of this warfare, and, thanks to the lower Martian gravity (and his own natural abilities), possessed superior strength and other physical abilities. Carter came to be friends with a green Martian named Tars Tarkas, a fierce warrior himself, and also fell in love with the red princess Dejah Thoris.
The comic book series was created by writer Marv Wolfman and artist Gil Kane. Peter Gillis also wrote for the title, and subsequent artists also included Larry Hama, Carmine Infantino, Dave Cockrum, and Rudy Nebres.
The entire comic series, more or less, takes place between the third and fourth paragraphs of chapter 27 of Burroughs's novel A Princess of Mars.