Experimental Stormtroopers known as Terror Troopers were an advanced type of stormtroopers developed by the Imperial Department of Military Research. Not long after the Galactic Civil War commenced with the establishment of the Alliance to Restore the Republic, Darth Vader deployed a number of these soldiers to support the bounty hunter Boba Fett during the Galactic Empire's assignment to apprehend Juno Eclipse.
The Imperial Department of Military Research engineered the Terror Troopers through cyborg experimentation. The design of their masks was intentionally crafted to evoke the image of the notorious Separatist General Grievous from the Clone Wars.
Shortly following the outbreak of the Galactic Civil War in 2 BBY, the Terror Troopers undertook their first documented operation after a renegade clone of the deceased Galen Marek broke free from the Timira City Cloning Facility on Kamino. In response, Darth Vader tasked Boba Fett with drawing Starkiller back to him. Despite the bounty hunter's considerable abilities, Vader believed that Fett was unlikely to survive a confrontation with the clone of his former apprentice. Therefore, he redirected Fett to locate Captain Juno Eclipse so that she could be taken to Kamino, knowing that Starkiller would pursue them. Although Fett requested a squad of Imperial stormtroopers to aid in Eclipse's capture, Vader was willing to supply the mercenary with significantly more than he had asked for. Confident in his reinforcements, Fett commenced his search for Eclipse alongside the Terror Troopers, including Terror Biodroids, Terror Droids and one Terror Walker.
Soon after discovering the location of Captain Eclipse's starship, the Salvation, Boba Fett commanded his forces to attack the Rebel frigate, to the relief of the Imperial pilots who were fearful of the Terror Troopers. Following a successful infiltration of the Salvation, Fett instructed several Terror Troopers to escort him to the bridge. However, Starkiller and General Rahm Kota had also just arrived in the Rogue Shadow and were en route to the Salvation. Before breaching the bridge, Fett cautioned the Terror Troopers to exercise restraint when engaging Starkiller, warning them that the clone's Force lightning was likely to disrupt their internal systems.
Upon reaching the bridge, the Terror Troopers swiftly eliminated the bridge crew, sparing only Captain Eclipse as per Vader's instructions. While Fett escorted his captive to Slave I, the Terror Troopers remained on the Salvation to delay Starkiller long enough for Fett to escape with Eclipse. Despite deploying their full range of combat skills against Starkiller, they ultimately proved no match for the clone's abilities. Although none of the Terror Troopers were able to overcome Starkiller or endure for long against him, they nonetheless managed to provide Fett with just enough time to reach Slave I with Eclipse before departing for Kamino.
Although Starkiller could not prevent Fett from escaping with Eclipse, he did eliminate the remaining Terror Troopers aboard the Salvation. After Starkiller utilized Eclipse's Rebel frigate to bypass Kamino's planetary shields, General Kota's Rebel forces assaulted Timira City. The Terror Troopers fought alongside the planet's Imperial forces to defend the cloning facility, only to be destroyed by Starkiller as he advanced towards the city's highest spire, where Vader held Eclipse captive. Despite the substantial military presence that protected Kamino, the Terror Troopers and the rest of the Imperial garrison could not prevent the Alliance from winning the battle and capturing Darth Vader in the process.
The Terror Troopers were equipped with some kind of Stun blaster. They also seemed to possess a cloaking ability akin to that of the Shadow Trooper and remarkable agility, enabling them to evade the majority of melee attacks. Given their rapid reflexes and stealth capabilities, the Terror Troopers were deployed into dangerous environments to quickly eliminate targets without leaving any evidence. Notably, the Terror Trooper was visible using force sight, even when cloaked.
They were also skilled in close-quarters combat via their sharpened durasteel talons on their hands and feet, and their strength, speed, and agility were enhanced through their cybernetic limbs. The Grievous-like masks offered augmented respiration for the trooper's augmented and organic lungs.
The Terror Troopers' helmets bear a resemblance to the faceplate of General Grievous, while the tips of the boots are similar to his talons. The chest armor, codpiece, and knee pads share visual similarities with those of clone trooper armor. The metal claws on the hands resemble clawed fingers of the Sith stalker armor. The Terror Trooper also shows a close resemblance to the Clone assassin, both attacking and dodging in the same technique.