Gahan is the Jeddak of Gathol and one of the protagonists of the book The Chessmen of Mars. In this book he marries Tara, the daughter of John Carter and Dejah Thoris. As a married couple, Gahan and Tara have a daughter named Llana who is the granddaughter of John Carter and Dejah Thoris.
Gahan and Tara first meet in the palace of John Carter. Gahan follows the Barsoomian custom of falling in love at first sight with Tara of Helium and proclaims his love for her following The Dance of Barsoom. Unfortunately, she is far less impressed by him, dismissing him as a mere clothes horse. The next day she angrily sets out in a private flier to have some private time, while Gahan returns to Gathol on board his own flier, the Vanator. Both fliers are caught in a severe storm. Gahan rescues one of his men from falling overboard, but falls overboard himself as a result, and his crew loses sight of him. After weeks of wandering around, Gahan finds himself in Bantoom, land of the Kaldanes, and discovers Tara is also there, about to be taken to Luud. Gahan breaks into the tower of Luud and teams up with the Kaldane Ghek to free Tara. The three succesfully escape in Tara's flier. Tara does not recognize Gahan, and he, remembering how she loathed him during the dance he introduces himself to her as Turan the Panthan.
After escaping from Bantoom, the three heroes end up in Manator. Gahan sneaks into the city to find food and water, but falls into a trap and is captured. Ghek and Tara soon follow. They learn Manator is ruled by the cruel Jeddak O-Tar. While a prisoner, Gahan meets O-Tar's son A-Kor and learns from him that Tara is also a prisoner. During a mock trial where Tara is accused of Corphalism (witchcraft), she, Gahan and Ghek escape. They meet the old man I-Gos, who seperates the two by locking Gahan into a room. Tara is soon after recaptured and made into a prize to be won during the next games of living Jetan. Gahan changes his name again, this time to U-Kal, so he can participate in the games as well. His team wins the games when Gahan slays the opponent's chief U-Dor. Jeddak O-Tar however, does not approve of Gahan's victory, since he wants to marry Tara himself.
When Gahan meets his old friend Tasor, who is now a prisoner in Manator, they make plans to help A-Kor overthrow his father. He finds more people willing to help him with this task. They spread word of O-Tar's cowardice, resulting in O-Tar being challenged to enter a room under the palace where the body of the Jeddak O-Mai lies. When O-Tar goes there, Gahan ambushes him and takes his place during the wedding. On the wedding day the slaves start a revolt while A-Kor and his followers storm the palace. O-Tar commits suicide and Gahan finally reveals to Tara who he really is. The two are married shortly after.