An agent of the feared Imperial Security Bureau, Kallus was a veteran of numerous operations against rebellious planets of the Empire. He was also a cunning tactician, able to outthink the Empire’s enemies. But the ruthless agent struggled to bring Hera Syndulla’s rebel cell to justice on Lothal.

In the Empire’s endless drive to squash all rebel threats, a trap was set for the Ghost team. Luring the motley crew to a construction module orbiting Geonosis, Kallus and squads of stormtroopers were waiting for the freedom fighters. In the ensuing battle, the ISB agent and Zeb Orellios were cut off, ending up in an escape pod together. They crash landed on a nearby moon -- two bitter enemies, stranded together. Kallus’ leg was broken in the crash, temperatures were frigid, and a large beast called a bonzami — and its friends — posed various threats. In the end, they had to work together to survive, and came to a newfound respect for each other. When the Ghost arrived, Kallus decided to wait for the Imperials; but he heard how warmly Zeb was greeted by his friends, and found himself very alone when back with the Empire.

Following his interactions with the Ghost crew, Kallus defected to the rebellion and operated under the name Fulcrum. For a time, he successfully helped the rebellion in secret, but Grand Admiral Thrawn eventually deduced that a traitor was in his midst. When the search intensified, Kallus tried to implicate Lieutenant Lyste; while it initially appeared to work, Thrawn knew that Kallus was the spy and looked to turn this betrayal to his advantage.