In 1 BBY, Rosco wanted to become a stormtrooper, but failed the entry exam. Bitter that he would never be able to serve the Galactic Empire, Rosco sought to hurt the Empire and joined the Alliance to Restore the Republic.
Rosco had friends in the Rebel base of AX-456, including Ors, and lost many of them during the Imperial raid.
He later went on to work with Rebel agent Jan Ors and Ris Waller on the luxury liner Star of Empire for a "recruiting trip". Ors, who had been present during that raid, was ready for retribution in the battle field, and expressed her disappointment to Ross. He answered that he also lost men there and wanted the same, but it was not the right time; he explained that the orders came from "the top" because Ors needed to "cool her engines", and was considering that mission a great opportunity to travel onboard a cruiser.
Ors noticed that Imperial officer Kyle Katarn was onboard and he started chasing her; the three of them coordinated an improvisional plan to capture him. Rosco was in the storeroom when Waller notified him over the comlink that he was on the way there. Ors arrived and soon after followed by Katarn, who immediately was immobilised by Rosco's choke hold; Katarn was unable to pry his strong arm. Right then Waller showed up.
Ors ordered him to shove Katarn into the storeroom. Rosco threw him on the floor, and unexpectedly, standing up, Katarn launched a backward kick hitting Rosco's knee, who, to his surprise, didn't feel pain at all. Rosco would retaliate if Ors didn't stop him, saying that he had guts to take AX-456, and also to spare their lives. Rosco showed scepticism with Katarn's word that he will let them be if they let him go.
Their operations were noticed by a bounty hunter and soon Katarn warned Ors that the Imperials knew about them and would soon come. Ors ordered them to go to the hangar deck and prepare the Truly Sorry. He was armed with a blaster carbine ready to use it, waiting for Jan and A-Cee but Katarn showed up first.
He was surprised when Katarn, as if he were a leader, ordered him to cover Jan and the droid while he cranked the ship up; he pointed out that his piloting skills entitled him to arrange the things. Calling him "Admiral" Ross asked how he'd open the hangar's massive and Katarn ensured that he'd handle it; by threatening the Hangar Control.
While the doors were opening, Jan entered the hangar and Rosco notified Kyle over the comlink. She was followed by a Rodian and Imperial soldiers. They exchanged fire with Rosco. Jan collapsed to the floor because of the lack of oxygen. Rosco already wore an emergency oxygen mask and didn't need to hear Kyle's suggestion to help her. He picked her up and as he turned a stray piece of paper whipped his face. Those moments he wondered whether the ship was there or if Kyle left without them, but he had already approached them and Rosco stepped on the ramp, and were lifted inside.
While Rosco was recovering, a ship pursued them, but out of coincidence was destroyed because of an internal explosion – A-Cee was on board and his self-destruct mechanism was activated – they safely made it to the New Hope.
Rosco had a barrel-like build with extremely strong arms; when he threw a choke hold on Katarn, he was unable to pry his arm, as it was like bending a durasteel. His tiny eyes were blue and his nose had been flattened by beating and brawls. When Katarn met him, his blond hair had a crew cut.
In the audio adaptation of Dark Forces: Soldier for the Empire, he was voiced by .