The IG-88 series assassin droid was designed and manufactured by Holowan Laboratories and funded by Imperial Supervisor Gurdun. Four prototypes were to be made, equipped with the newest technology, weapons, and equipment. The activation of the first droid, however, brought unexpected and potentially dangerous results. As soon as IG-88 was activated, sentience spread through its brain like wildfire. It grew far beyond what it was designed to do, despite the frantic efforts of the Holowan scientists to stop it. As IG-88 rose, an engineer dashed for the emergency alarm. The assassin droid snatched a disembodied droid arm off a nearby table and threw it as a projectile at the panicked engineer. The arm tore through his body and out his breastbone. The overseer of the project grabbed a blaster and fired, only to have IG-88 reflect it back, killing her. After quickly dispatching the other 13 scientists, IG-88 activated the other 3 assassin droids only to find that they were not sentient. He observed the carnage and smashed machinery and came to a conclusion. Quickly, he downloaded his entire personality into the other 3 droids, creating IG-88B, IG-88C, and IG-88D. Together, the four droids blasted their way out of the laboratory and stole a ship, headed for Mechis III, the galactic center of droid manufacturing.
Upon reaching Mechis III, IG-88C overrode the entire planetary defense system, while IG-88D downloaded full details of the planet, and IG-88A transmitted his sentience into the main hubs of the droid manufacturing, taking over vast electronic complexes. The four droids then sent a signal to several droids on the planet, making them rise up against the few humans on-planet. Soon the IGs had eradicated all human life on the planet, and controlled all of the droids. The four assassin droids made sure every thing would run exactly the same, not changing the outward appearance at all. Mechis II was theirs.
The IG-88s enhanced the programming of all the droids so that they had embedded sentience programming. IG-88 would soon be able to replace the "cumbersome biologicals" with machines like himself. When the arming code would be transmitted, the sentience programming would become active and all the droids would rebel against the biologicals. Then, the galaxy would be under IG-88's palm.
Soon, however, an Imperial spy directed questions toward Mechis III, making the IG assassing droids very nervous. They soon decided to make an obvious trail far away from Mechis III. As a result, IG-88B became a bounty hunter. IG-88B soon made the IG-2000 to serve as its bounty ship. It left the planet, looking for its first bounty. Very soon, it had earned a name for itself by accepting a small bounty and completely annihilating the target and the target's company.
Meanwhile, back on Mechis III, the other three IG droids were in for an unpleasant surprise. Darth Vader had landed on the planet, demanding to speak with the supervisor. Using video clips, the assassin droids were able to convince the Dark Lord that all was well with his recent order of Imperial Probe Droids. Of course, the probe droids were sentient as well, and the relayed all information collected to the assassin droids.
IG-88B responded to Vader's call for bounty hunters to find Han Solo. The assassin droid planted a tracking device on each of the bounty hunters' ships, figuring that it would let them find Solo and then steal him away. While on board the Executor, IG-88 had downloaded all the files in the computer, learning about the construction of a second Death Star. It decided that it would download its personality into the computer core of the new Death Star, thus controlling the most powerful weapon in the galaxy. IG-88B raced back to Mechis III to shate its ideas with its three counterparts.
Upon hearing the information, the IG-88s decided they would duplicate the computer core and ships carrying or escorting it. They would then switch the convoys, and deliver the core inhabited by their personality to be installed into the Death Star. As the Death Star core replicate was being made, IG-88B learned that Boba Fett had found Han Solo, and was currently en route to Bespin. It quickly departed Mechis II on an intercept route. As the droid landed on Cloud City, it located Fett in the lower levels of the city, no doubt preparing a trap for Solo. IG-88 travelled to the lower levels to kill Fett and steal the bounty. As it passed through a metal hatch leading to the room where Fett was, ion cannons blaster into the droid, causing it to lose control of all systems. Boba Fett emerged from the shadows, triggered two of the assassin droid's concussion missiles, and left. The missiles exploded, tearing IG-88B apart.
IG-88C and IG-88D recieved news of their fallen comrade and departed in pursuit of Boba Fett while IG-88A supervised the completion of the Death Star mission. IG-88C waited in orbit of Tatooine as IG-88D waited to drop out of hyperspace. Soon, the Slave I appeared from hyperspace. As soon as Fett saw the IG-2000 lying in wait, he shot all his weapons, easily destroying the vessel and IG-88C. Right away, IG-88D came out of hyperspace, racing towards the Slave I with weapons blazing. Fett hurtled toward the planet witht he IG-2000 right behind. Then, Boba turned on his inertial dampening, stopping his ship and watching IG-88D race past him. The human bounty hunter fired, destroying IG-88D.
Meanwhile, IG-88A had switched the Death Star computer convoy, and soon, the computer with IG-88's personality was installed in the Death Star. IG-88 waited a little too long, and just before it sent the arming code to begin the droid revolution, the second Death Star was destroyed, taking the last of the IG-88 assassin droids with it.