Lesim held the Imperial Army rank of major during the Galactic Civil War. In 4 ABY, while stationed on an All Terrain Armored Transport patrolling the Forest Moon of Endor, Lesim encountered Rebel Alliance Commander Luke Skywalker. Skywalker surrendered himself to Lesim and his stormtroopers, requesting to be taken to the Dark Lord Darth Vader on the moon. Lesim, believing the capture of the famous Rebel would result in his promotion to general, desired a hologram with Skywalker before delivering him to Vader.
During the Galactic Civil War, Lesim served the Galactic Empire as an officer fighting against the Alliance to Restore the Republic. By 4 ABY, he had attained the rank of major within the Imperial Army. In that year, as the Battle of Endor began, Lesim commanded a group of stormtroopers from an All Terrain Armored Transport walker patrolling the Endor moon. Commander Luke Skywalker of the Rebel Alliance approached Lesim's stormtroopers and voluntarily surrendered, seeking to be delivered to Darth Vader, the Dark Lord of the Sith, on the moon. Using a mind trick through the Force, Skywalker convinced the troopers to bring him to their commanding officer. The Imperial soldiers then escorted the Rebel to Lesim in the walker's transport section, presenting his confiscated lightsaber to the major.
After carefully observing his captive for a few moments, Lesim stated that he recognized Skywalker from Imperial Intelligence files and believed capturing the famous Rebel would lead to a promotion to general. He instructed Arno, one of his men, to retrieve his imager so he could take a hologram with Skywalker. Although Lesim followed Skywalker's Force-persuasion to deliver him to Vader, he still wanted to take the hologram with his prisoner beforehand. Ultimately, another Imperial officer, Commander Igar, personally escorted Skywalker to Darth Vader on Endor. Alliance historian Voren Na'al later compiled the story of Skywalker's capture on Endor, using reports gathered from both Skywalker and captured Imperial troops following the Battle of Endor.
Michael Stern created Lesim for the short story The Capture of Luke Skywalker, which was published in the 1990 West End Games sourcebook Galaxy Guide 5: Return of the Jedi.