Early in his career as an Imperial Security Bureau agent, Kallus was given command of a platoon that was deployed to the planet Onderon to bring peace to that planet. On a routine patrol the platoon ran into a rebel, a Lasat mercenary who worked for Saw Gerrera. Kallus was incapacitated by the first blast. After regaining consciousness, he witnessed the Lasat calmly walking through the smoke, killing the rest of the platoon one soldier at a time. Although the Lasat mercenary killed all of Kallus' comrades, he spared the agent's life. Kallus later recounted this incident to his long-time rebel adversary Garazeb Orrelios, when the two were stranded on Bahryn, an icy moon that orbited the planet Geonosis.