Junus held the rank of captain within the Galactic Empire and was the commanding officer of the garrison stationed at Fortress Vader. This fortress served as the personal abode of Darth Vader, the Dark Lord of the Sith, and was located on Mustafar, a planet characterized by its volcanic activity. In the year 12 BBY, Kkkt, a Southern Mustafarian Father, spearheaded an army of Mustafarians mounted on lava fleas with the objective to destroy the fortress. Responding to this, Junus reached out to Vader, who was in close proximity, and advised the evacuation of their forces due to the Mustafarian encirclement of the fortress.
Vader dismissed the situation as another lava flea incursion, a frequent nuisance since Fortress Vader's construction commenced, and instructed Junus to handle it independently. However, Junus maintained that the assault posed a significant threat, urging Vader to personally assess the situation. Consequently, Vader emerged from the cave to examine the danger and was compelled to engage the invading Mustafarian army in combat. Despite Vader's intervention, the Imperial garrison was ultimately annihilated. Junus's primary language was Galactic Basic Standard.
Junus's vocal portrayal occurred in Darth Vader (2017) 23, a comic authored by Charles Soule, with illustrations by Giuseppe Camuncoli. Marvel Comics published it on November 14, 2018.