- "I just…I just wanted something back. I guess I felt like…like they owed me."
- ―Chopper, on the Confederate battle droids
An aggressive soldier, Chopper was scarred during a battle droid ambush on Geonosis, and he came to hold a personal grudge against his Separatist adversaries. In 21 BBY, he was dispatched with a Jedi-led contingent of the Grand Army of the Republic to liberate the planet Christophsis from the Confederacy. When the Separatists foiled the Republic's attempt to ambush them, Chopper and his unit were forced to retreat with the rest of the Republic troops back to their base. While there, Chopper secretly made war trophies out of droid fingers pilfered from the battlefield, an exploit he was later forced to disclose when his superiors, Clone Commander Cody and Clone Captain Rex, interrogated his unit to root out a potential Separatist spy. Although Slick framed Chopper to be the enemy agent, the Sergeant himself was revealed to be the turncoat and was apprehended after sabotaging the Republic's military supplies.
- The Hidden Enemy (First appearance)