Jester was a clone trooper who served in the Grand Army of the Republic during the Clone Wars. He was known in his squad for cleaning their DC-15 blaster after every mission.
During the Battle of Christophsis, Captain Rex and Commander Cody pinpointed an irregular wavelength in external communications to Sergeant Slick's barracks, fueling their suspicion that someone in the platoon was a Separatist spy. Consequently, the two officers called Jester and the other members of their unit back to their quarters to individually interrogate them about their whereabouts earlier that evening. Jester was nervous about speaking to his commanding officers, but fellow trooper "Sketch" vouched for Jester's habit of regularly cleaning his blaster. When Jester presented his freshly scrubbed weapon to Cody as evidence, he was cleared of suspicion.
Eventually, Slick was revealed to be the spy and escaped from the barracks, following which he sabotaged the Republic's gunships, AT-TE walkers, and weapons depot. When trooper "Gus" spotted Slick heading for the base's command center, Rex and Cody ordered Slick's unit to secure the perimeter. The two officers thereafter managed to detain Slick.