|The information in this article comes from Mars: The Home Front and is not written by Edgar Rice Burroughs.|
Bas-Ok was an old army officer from Gathol. He is described by John Carter as being an old man, well beyond his prime, but still dressed in the harnass of a fighting man.
At some point prior the start of Mars: The Home Front, he was taken captive by the Sarmaks who wanted to drink his blood. While being imprisoned in his cell, he meets John Carter and Kar Komak, who had been captured by Sarmak allied Red Men while looking for Dejah Thoris. From Bas-Ok, Carter learns the Sarmaks are in the middle of invading Jasoom. Every day they launch a cylinder carrying weapons, machines and Sarmaks to the planet.
John Carter takes Bas-Ok with him when he escapes from his cell and plans to rally all his allies against the Sarmaks. Bas-Ok eventually reveals himself to be a traitor however, and tries to give John Carter to the Sarmaks. John Carter kills him for his betrayal. Exact details surrounding this event are unknown since Carter only briefly mentions it to his nephew.