The first ever mass-produced combat MS, developed by the Principality of Zeon. Although they were produced in large numbers in preparation for the war, they faced such issues as poor generator output and restricted operational time or reduced mobility due to overheating, and one fighting began, the enhanced Zaku II ended up being Zeon's primary mobile suit. As the Zaku II proliferated, the Zaku I became relegated to use by resupply units or to test new special weapons, quickly being termed the "Old Zaku" before having ever distinguished itself in combat. It was actively used all the way to the end of the war, and had a plethora of combat modifications and personal customizations. This particular machine belonged to Garret Schmitzer, commander of the MS tactics test team known as the Midnight Fenrir Corps. It incorporated various modifications, increasing its versatility, and allowing it to perform at a higher level overall.