Fal Sivas is a rival of Gar Nal, another Zodangan inventor. At the start of the story, both inventors have been working for years on spaceships capable of interplanetary travel (something that has not been achieved yet upon Barsoom). They frequently spy on each other and steal each others ideas whenever possible. Fal Sivas has also stolen many other ideas from other rivalling inventors, killing them afterwards so he could take all the credit. His dream is to fly his spaceship to Thuria once it is competed in hopes of finding huge supplies of platinum and other valuables there. However, he does not have the courage to take his ship for a test flight.
One of Fal Sivas' most remarkable inventions is a mechanical brain, which allows his ship to fly and carry out missions without the need of a pilot. To develop and perfect the brain however, Fal Sivas has conducted many cruel experiments on the living brains of his slaves. The brain can be commanded through telepathic thoughts.
Fal Sivas first appears in the story when John Carter goes undercover in Zodanga to try and take down the assassins guild there. He volunteers to become the bodyguard of Fal Sivas, proving his worth by defeating Rapas the Ulsio in a battle. In Fal Sivas' home, Carter meets the slave girl Zanda and learns about Fal Sivas' cruel experiments. When Fal Sivas demonstrates Carter his ship, Carter finds out he too can command the mechanical brain through telepathy (something Fal Sivas thought only he could do).
When Dejah Thoris is abductect by Gar Nal and taken to Thuria, John Carter steals Fal Sivas' ship, freeing or killing his slaves and defeating several of Fal Sivas' henchmenin the process. After this incident Fal Sivas disappears from the narrative untill the last chapter, in which he manages to call his ship back to Barsoom (despite the fact that it was on Thuria at the time) and keep the mechanical brain from accepting anymore of John Carters' commands. He then tries to hide for John Carter in the house of Gar Nal, forming an uneasy alliance with his rival, since that is the last place John Carter would seek him. Naturally, John Carter finds him there. When Gar Nal reveals Dejah Thoris is still on Thuria, Carter threatens to kill Fal Sivas so he can reclaim controll of the ship and rescue her. Fal Sivas begs Carter to spare him and promises to give controll of the ship back to him. The situation is solved when Dejah Thoris is revealed to have been in Gar Nal's house all along. Gar Nal is killed for his treachery, but Fal Sivas' fate is not revealed.