You will find below a picture featuring the main characters of John Carter, with their counterparts in Princess of Mars. Princess of Mars, what is it?
If John Carter is indeed the first theatrical adaptation of A Princess of Mars by Edgar Rice Burroughs, it's not the first adaptation in all. This "honor" is bestowed to a direct-to-video movie released in 2009, Princess of Mars. It was produced by the Asylum company, which made a specialty of being "inspired" by movie successes of the moment to release their own cheap versions. When Transformers is released, they make Transmorphers. When Marvel releases Thor, Almighty Thor lands on SyFy Channel... When Avatar triumphs in 2009, Asylum is making Princess of Mars! Why? Because James Cameron confessed during interviews that he had wanted to shoot "an adventure à la Burroughs". It's all that was necessary for a Mark Atkins to get to work. He will be writer, director, director of photography and editor, an abundance of titles unusual even for an Asylum production, which can lead to believe that maybe, maybe, said Mark Atkins is perhaps a fan of the novels!
I write "maybe he's a fan" because it doesn't necessarily translate in the movie. If Antonio Sabato Jr isn't that bad in the movie at all (he proves if necessary that a character closer to the novels', without a damaged past, work just fine on screen), Traci Lords is completely awful as Dejah Thoris, and has zero chemistry with her onscreen partner, a shame for what is essentially a love story! With an abysmal budget, the Tharks are plain normal-sized humans, without any additional limb, dressed as Roman soldiers, with rubber maks. The CG creatures are pretty generic (giant spiders, ostriches lookalikes as mounts) and doesn't look like those of the novels at all. Only the giant bugs exist, the Siths (another item borrowed by George Lucas for Star Wars), and those only appear in the third novel! The direction is uninspired, the fights are laughable, and only a few SFX shots of airships are any kind of good. It's fairly ironic that A Princess of Mars also had two adaptations, as far from each other budget-wise as they can be, namely the cheapest and the most expensive possible!
Princess of Mars is only to watch out of completeness, and nothing else. A funny bit of trivia, Matt Lasky, who plays Tars Tarkas in the Asylum production, had been hired on John Carter when it was shot in the Utah desert, as a Young Thark Warrior! As for many extras in Hollywood, the part ended up uncredited, but it's still mentioned on the IMDB page of John Carter. The actor will probably remember for a long time seeing the walk of his Asylum character mimicked off-camera by Andrew Stanton's Tars Tarkas, Willem Dafoe!