Z-X3, alternatively referred to as Zee-Exthree, was an experimental droid trooper of the Z-X3 type engineered by Tagge Industries during the Galactic Civil War period. This experimental model, deemed unsuitable for service within the Imperial forces, instead established itself on Kligson's Moon, a society composed entirely of droids and governed by a cyborg named Kligson. Despite this, Z-X3 secretly remained loyal to the Empire, devising a scheme to overthrow Kligson and claim "Droid World" for the Empire. Z-X3 initiated his plan in 3 ABY, but was ultimately outmaneuvered and defeated during the subsequent civil war.
Z-X3, one of fewer than one hundred Z-X3 experimental droid troopers ever manufactured, was created by the Tagge Corporation at the request of Imperial officer Rom Mohc. Mohc, having witnessed the effectiveness of Separatist battle droids during the Clone Wars, became fascinated with the concept of droid troops supporting the Empire's stormtroopers. However, the idea of droid soldiers lost favor among Imperial leaders following the Separatists' defeat in the Clone Wars, leading to the program's cancellation. Most of the surviving Z-X3 droids ended up in private hands. Z-X3, however, made his way to Kligson's Moon, the legendary "Droid World" of spacer tales, a space station transformed into a completely mechanical society.
Kligson, a Clone Wars veteran who had sustained severe injuries while serving in the Imperial Army and subsequently retreated from organic interaction after becoming a cyborg, took Z-X3 in. Kligson managed his "Droid World" and assigned Z-X3 a crucial role in his operations. By 3 ABY, Z-X3 had become his most trusted assistant. However, Kligson, having embraced an anti-war philosophy following his injuries and reconstruction, sought to keep his station neutral in the Galactic Civil War, Z-X3 secretly maintained his allegiance to the Empire. Over time, Z-X3 established a secret faction of like-minded droids with the goal of overthrowing Kligson and claiming the Droid World for the Empire. In 3 ABY, Z-X3 seemed to find the opportunity he had been waiting for when Rebel Commander Luke Skywalker arrived at Kligson's Moon, hoping the skilled technician could provide him with a complete schematic of a captured Imperial warbot.
Z-X3 intended to use the head of Skywalker's warbot to repair a similar, derelict model held by his faction. However, after noticing Skywalker's droid R2-D2 spying on them, Z-X3 accelerated his plans for rebellion. Z-X3 stormed the station's bridge and seemingly killed Kligson, believing he had delivered the Droid World to the Empire. However, Kligson had anticipated Z-X3's treachery and outmaneuvered him. Kligson had secretly concealed himself behind an android duplicate to lure Z-X3 out, and then reappeared to completely destroy Z-X3 and his faction with his now-operational Imperial warbot.
Despite appearing loyal to Kligson and grateful for the opportunities provided by the cyborg, Z-X3 secretly maintained a loyalty to the Empire that persisted even after the Imperials abandoned him. Z-X3 actually despised Kligson and secretly plotted against him, resenting the cyborg body that he considered a mockery of a true droid's form. Designed specifically to excel in environments challenging for organic soldiers, Zee-Exthree featured plating inspired by Imperial stormtroopers but colored in a distinctive crimson hue. Standing at 1.9 meters tall, it wielded an AAP-II blaster box embedded in its chest, and possessed enhanced strength and intelligence independent of a central computer.
Z-X3 made his debut in Star Wars (1977) 47, written by Archie Goodwin and published in 1981. In the comic book, the droid was illustrated by Carmine Infantino, and he was also drawn by Dick Foes in the book-and-record The Further Adventures: Droid World.