XT-8 was a XT labor droid which had been modified to be an assassin droid. He was painted a dull green and given photoreceptors which glowed with an evil, red light as well as a vocabulator which produced a buzzing, barely coherent voice. XT-8's personality matrix was crude even for an assassin droid by the time of the Galactic Civil War, though the XT model was high technology around 20,000 BBY. During combat, XT-8's chest panel would swing apart to reveal a submachine gun which could fire 180 degrees to the front.
XT-8 was part of the bounty hunter Leshy Drobo's crew and helped him capture Roni von Wasaki. While Drobo and Gammid provided a distraction, XT-8 sneaked up behind Wasaki and stunned him. Once Drobo had loaded Wasaki onto the Starkiller, now frozen in carbonite, XT-8 was tasked with piloting the ship to receive the bounty. However, Wasaki managed to influence Drobo to free him through use of the Force. XT-8 soon found out about this and confronted Drobo in the engine room, firing on him and killing him while also damaging the hyperdrive. This caused the ship to drop to realspace and the journey that would have taken but 30 days in hyperspace now dragged on for over 20,000 years. During all this time, XT-8 thought only of delivering his cargo.
Sometime during the Galactic Civil War, however, a ship containing a group of Rebels, one of them being a Force-sensitive, dropped out of hyperspace near the Starkiller. When they attempted to dock XT-8 fired upon them but, as the ships had over 20,000 years between their construction, the Starkiller was easily overpowered. The group then proceeded to board the ship and, when they entered the cockpit, were fired upon by XT-8. The group then disabled the droid, ending his mission once and for all.