Origin
Gor Mordas is the son of Kil Gor, a fierce warrior who slew many Tharks during the Battle of the Face of Barsoom. As he grew older, Kil Gor became ashamed of the massacre and grew silent. Upon discovering that there was almost no historical reference of the battle in the books, Dejah Thoris organized a trip with her friends to the battlefield.
Gor Mordas, a pilot himself, wanted to prevent Dejah from discovering the truth about his father’s role in the battle and pretended the air ship got broken on the way. He landed the party at an uninhabited site. Unknown to him, the site was used by White Apes. The White Apes slaughtered all but Dejah Thoris and the pilot, who had flown off.
Dejah had mentally contacted her son Carthoris, who came to rescue her. Dejah still wanted to see the battlefield. On her way to it, Gor Mordas contacted her and confessed to her why he did what he had done. But also that he had no idea that White Apes were on the site. As punishment for his deeds, he landed the airship on the same site, probably to let himself be killed by the White Apes.