Koob was part of the Stinger Mantis team and a comrade of Cal Kestis, whom he first encountered on Norsid. After a Haxion Brood bounty hunter ambushed the Jedi, Koob and his twin sister, Lizz, intervened, saving Cal by throwing the hunter into a mine shaft, which led to a strong friendship with Kestis.
Koob was well-known within the crew for his large appetite, with Gabs joking that he had consumed their prey during a mission that took place on Carida.
Saw Gerrera dispatched him, along with Kestis, Lizz, Gabs, Bravo, and the new member Bode Akuna, on a mission to Coruscant. Their objective was to extract intelligence from Senator Daho Sejan by impersonating members of the Coruscant Security Forces, with Kestis being presented as a prisoner to the senator. Although the plan was initially successful, the Ninth Sister launched a surprise attack during their escape, and killed the senator. Koob and Lizz attempted to engage the Ninth Sister, but they were killed as a result. Cal reflected sadly on the deaths of Koob, Lizz, and Gabs shortly afterward, and properly mourned them—as well as the recent death of Bravo—once they reached the safety of hyperspace.
Despite their ferocity and power in combat, Koob and his sister displayed deep affection and protectiveness towards their friends. Koob was seen affectionately patting Cal on the back (and messing up his hair) during their reunion on Coruscant, while Lizz embraced the Jedi. Both twins fearlessly charged at the Ninth Sister in a doomed attempt to protect their friends in hand to hand combat.
The twins communicated exclusively in Huttese, but they possessed a complete understanding of basic.