During the Galactic Civil War, Lyle Kullan infiltrated Rogue Squadron for the Galactic Empire and flew a T-65B X-wing starfighter as Rogue Four, alongside Commander Luke Skywalker during an attack on an Imperial shipyards in the Taris system. The squadron's mission was to fend off the TIE fighters, while A/SF-01 B-wing starfighters from Blade Squadron bombed the shipyards. Kullan was frustrated by fellow pilot and rookie Ibti Myrak, who argued with Skywalker and refused to stay in formation. Eventually, this led to an argument between Kullan and the rookie, when Kullan was about to shoot an enemy TIE, Myrak impatiently cut in front of his X-wing and took the shot instead, nearly crashing into Kullan, causing Skywalker to chastise both pilots. Shortly after, the B-wings released their bombs and destroyed the shipyards. Back on Home One, Kullan and the other pilots tried to confront Myrak about her reckless behavior, but the rookie wouldn't listen and stormed off.
Three days later, Draedan pirates attacked the Alliance Fleet in the . Kullan and the rest of Rogue Squadron launched in their X-wings to protect the cruisers. Against orders from Rogue Leader, Myrak left formation and chased a pirate vessel that attempted to escape, which led to her being ambushed. Kullan and the rest of the squadron came to her rescue and destroyed the pirates.
After the Rebels lost contact with Kullan while he was on patrol in the Valo system, Skywalker and the rest of Rogue Squadron launched in their X-wings, only to find themselves ambushed by an Imperial II-class Star Destroyer and its TIEs. Kullan turned out to be an agent for the Empire and orchestrated the trap in order to capture Skywalker. However, back on Home One, grounded rookie pilot Myrak found Kullan's secret messages and stole an X-wing to warn the Rogues. On arrival, Myrak destroyed the tractor beam projectors that had caught onto Skywalker's X-wing, releasing him and allowing the squadron to pursue Kullan. Before Kullan could dock his X-wing in the Star Destroyer's hangar, the Rebel fleet arrived under the command of Admiral Gial Ackbar, which forced the Star Destroyer to jump to lightspeed, leaving Kullan behind and taken into Rebel Alliance custody.
Lyle Kullan was a human male with black hair and dark-colored eyes and skin. He carried out the orders given by his squadron commander and worked towards the team goals of the unit, which contrasted with the singled-minded behavior of the rookie pilot Ibti Myrak, who disobeyed those orders, which Kullan didn't agree with. As a spy working secretly for the Empire, Kullan betrayed the trust of his fellow pilots and the Rebel Alliance, when he revealed his true nature to them.
As a pilot for the Alliance to Restore the Republic's Rogue Squadron during the Galactic Civil War, Lyle Kullan wore the standard orange flight suit, with white flight vest and life support equipment. He wore a white K-22995 light flight helmet adorned with red stripes and the Alliance crest in red.
Lyle Kullan first appeared in "Squad Goals, Part One," which was the first of a two-part comic story published in the eleventh issue of the 2020 comic-book series Star Wars Adventures. Written by Cavan Scott and illustrated by Manuel Bracchi, it was published on October 19, 2021.