WARNING SPOILERS BELOWGog is a young child Jorg and the Brothers meet under Mount Horus in Prince of Thorns. He is of the Leucrota, beings that have been mutated by the radiation that leaks from ancient nuclear weapons under the mountain. He was given as a sacrifice to the Necromancers under the mountain, but Jorg rescues him and his brother Magog from them. They did not have names when the band comes across them, and Jorg is the one who names them both.
Gog is fire-sworn, and strongly so. So much that the other Leucrota knew that his powers would tear him apart and everything around him eventually, which is the reason him and his brother were to be sacrificed to the Necromancers. Jorg takes a fancy to Gog, because his brother Magog was killed by the Necromancers and Jorg had also lost a younger brother.
In King of Thorns, Gog's powers were becoming more and more out of control, almost accidentally burning Jorg alive in his castle while they all slept. Jorg's advisors and the Brothers told him that he should kill the child before he harms anyone seriously, but Jorg is unable to accept this. He decides to take Gog to the Heimrift to see the fire-sworn named Ferrakind to see if the mage can help temper Gog's powers. On the way Jorg figures out how Gog controls and creates fires, which is from Gog explaining that "There's only one fire" and that he moves fire from one place to another.
Upon meeting Ferrakind, they discover that the mage has no intention of helping Gog, but to kill Gog and absorb his flame into himself and become stronger. When Ferrakind attempts to kill Gog, Jorg, and Gorgoth with flames, Gog redirects the flames to a spot that Jorg told him to previously. The intense heat coming from Ferrakind and Gog create a large tunnel to the underside of a large lake that floods the caverns they are in and kills Ferrakind. Unfortunately Gog was killed doing this.