Before meeting Valgarv, Jillas' people were nearly hunted to extinction. After being injured by humans and losing his right eye, Valgarv saved him and took Jillas' life into his hands. He was than partnered with Gravos Maunttop, who was also saved by Valgarv. The two became close and Jillas frequently referred to him as "Boss".

During the incident with Dark Star Dugradigdu, Valgarv, who had made an alliance with the overworlder Armace, ordered Gravos and Jillas to recover the five Dark Star weapons and bring them back to him. However, things became worse for Jillas when Gravos was assumed to be dead after losing control of Ragudo Mezegis and being blasted away by a Dragon Slave. Jillas swore vengence on the Slayers and eventually stole Gorun Nova from them by the use of psychological warfare.

Later, after everyone got separated and Valgarv was presumed dead, Jillas was rescued a fox named Elena and her son Palou, who called him "uncle". When Jillas discovered that the Slayers were still alive, he abandoned them and tried to get his vengeance again. When trying to kill the Slayers, Filia Ul Copt saved his life from getting caught in an explosion with one of his bombs. He was very grateful and referred to her from that point on as "Boss" as well, a name that Filia was not comfortable with.

After the final battle with Dugradigdu, it was revealed that Valgarv had been reborn as a pure ancient dragon and was adopted by Filia. Jillas, along with Gravos (who had only been literally launched into orbit by the Dragon Slave) became her partners and are helping her sell maces and pottery in a shop.

While Jillas is not skilled in magic or swordplay, he can still be a formidable opponent thanks to his experience with guns, gunpowder and other explosives. He also has a knack of exploiting the existing frictions within an enemy group to his advantage, managing to turn the Slayers against each other on one occasion.