Exo was a protocol droid aiding a spy within the ranks of the Rebel Alliance. This spy successfully acquired blueprints for a vital factory belonging to the Galactic Empire, who then tracked down and obliterated their hidden base. Exo and the spy were the only ones to survive this assault, making their escape via hyperspace. However, they were relentlessly pursued by Imperial Commander Tylux, who was determined to serve the Empire by succeeding. Capitalizing on Tylux's unwavering commitment to capturing the spy at all costs, the two rebels lured him into a carefully laid trap. This resulted in his Star Destroyer becoming disabled, which then allowed a rebel fleet to emerge and destroy it.
During the Imperial Era of the Galactic Empire's reign, Exo was in service to the Alliance to Restore the Republic, working alongside a human male operative acting as a spy. After the spy managed to uncover the schematics for a crucial Imperial factory, Commander Tylux, in command of the Star Destroyer known as the Bellicose, initiated an attack upon the rebel forces' base. This killing resulted in the deaths of all members of the cell except for Exo and the spy. The pair managed to escape into hyperspace aboard a U-wing, seeking refuge within an asteroid field positioned above a desert planet nearby.
Commander Tylux, fearing the repercussions from Sith Lord Darth Vader for his failure to secure the spy, pursued their vessel into the asteroid field. The spy then directed Exo to assume control of their starship as several TIE fighters gave chase. Surrounded by the pursuing fighters, the spy instructed Exo to pilot the U-wing into the atmosphere of the planet. Exo expressed hesitation due to the planet's severe sandstorms, but the spy insisted that it was their only remaining option.
Despite the perils presented by the sandstorm, Tylux dispatched his entire fighter wing to the planet's surface to pursue the spy. The storm compromised the fighters' sensors and caused their engines to overheat, which then allowed Exo and the spy to successfully escape the planet before their own engines suffered the same fate. The spy destroyed the remaining TIEs, but Tylux, unwilling to fail Vader, decided to continue the pursuit in his Star Destroyer, navigating through the asteroid field.
To set a trap for the relentless commander, the rebels flew their craft into the mouth of a nearby exogorth, with Tylux following close behind. The spy then blasted through the side of the creature, and Tylux's attempts to ensnare the rebel vessel using his Star Destroyer's tractor beam were thwarted by the numerous mynocks that had infested the exogorth. With the Star Destroyer rendered inoperable, a fleet belonging to the Rebel Alliance emerged from hyperspace above the planet, destroying the Imperial vessel and rescuing both Exo and the spy.
Exo, a protocol droid programmed with feminine characteristics, featured blue plating and yellow photoreceptors. During their efforts to evade Commander Tylux's pursuit, Exo displayed hesitation regarding her captain's plans and expressed panic concerning their situation as Imperial TIE fighters pursued them through the sandstorms of the desert planet. Exo shared the spy's astonishment at Tylux's unwavering determination to hunt them down.
Exo made an appearance in the comic titled Vader - Dark Visions 2, penned by Dennis Hallum, illustrated by Brian Level, and released by Marvel Comics on March 27, 2019.