Troopers of the Galactic Empire, specifically stormtroopers, who had been infected with the Sickness viral agent became known as Undead Troopers. A viral outbreak transpired between the Battle of Yavin and the Battle of Hoth. These troopers, after dying a painful death, transformed into unthinking, walking corpses driven by cannibalistic desires. Research indicated that Undead Troopers, due to the infection, moved slower than living humans, but displayed enhanced resilience to damage.
The Undead Troopers possessed the ability to communicate telepathically and learn, thanks to the virus. Functioning as a unified force, they demonstrated a willingness to organize into a lethal swarm, executing synchronized assaults on both Imperial and Rebel Alliance forces. Furthermore, they successfully reprogrammed and hacked turret controls and security systems in captured sectors to their advantage. This allowed them to reinforce seized bases against potential counterattacks, utilizing blaster cannons, walls, and shield generators to repel enemy engagements. Imperial scout troopers and Heavy Weapons Stormtroopers who succumbed to the illness were categorized as Scout Undead Troopers and Heavy Undead Troopers, respectively. Their skill and coordination earned them the moniker "Army of the Dead".
The Star Wars Legends novel, Death Troopers, marked the initial appearance of Undead Troopers, portrayed as undead stormtroopers infected by a Sith plague that originated in the days of the Old Republic. Later, they were integrated into canon through the mobile game Star Wars: Commander as "Death Troopers" during a limited-time campaign released in 2014. In a 2016 limited-time event for Star Wars: Commander, the Death Troopers were renamed "Undead Troopers," likely to prevent confusion with the newly introduced elite stormtrooper variant. This confusion was also exploited in-universe, with Emperor Palpatine leveraging fearful rumors of the undead "Death Troopers" to name the elite black armored variant.