During the Clone Wars period, specifically in its early stages, a mutant terrorist with significant genetic expertise, Zeta Magnus, engineered a clone army. This army was based on the genetic template taken from Sarsius Torne, a mercenary of the Thyrsian Sun Guard. Within his Rennek palace, situated in his Dark Worlds kingdom within the Unknown Regions, Zeta Magnus maintained hundreds of clones in a state of suspended animation inside specialized clone cylinders. Sarsius Torne personally trained four of these Sun Guard clones, who were then formed into a specialized unit known as Tark Squad. After a clone of Zeta Magnus achieved the subjugation of the planet Skye, Darth Sidious intervened. He assisted in disguising Tark Squad as clone commandos and strategically placed them on Kamino. Subsequently, they were assigned to accompany a Jedi strike team dispatched to Skye with the mission to arrest Zeta Magnus. Upon the Jedi's arrival at Magnus's fortress, the clones betrayed them, using stun weaponry to incapacitate them and deliver them to Magnus. However, the Jedi managed to escape, ultimately eliminating both Tark Squad and the Zeta Magnus clone. Despite the elimination of Tark Squad, the larger clone army created by Zeta Magnus remained hidden in the Unknown Regions.
Following the Battle of Endor, Andor Javin, a reporter working for NewsNet's TriNebulon News service, made a significant claim. He identified Lord Shadowspawn, an Imperial Warlord, as K'am'ir Zaarin, which he asserted was an alias used by Zeta Magnus. Javin further alleged that Shadowspawn/Magnus possessed a clone army and was collaborating with a clone of Grand Moff Tarkin.
The primary villain in the unreleased The Epic Continues storyline planned by Kenner Products was Atha Prime. Described as both a "genetic master" and the "architect of the Clone Wars," Atha Prime amassed a force of clone warriors that he then deployed to seize control of the fragmented remnants of the Empire after Endor, and to conquer planets recently freed by the Alliance to Restore the Republic. Abel G. Peña, in collaboration with others, attempted to integrate Atha Prime into existing canon in an article for Polyhedron magazine focusing on Imperial Warlords. This article, which ultimately went unpublished, sought to merge Atha Prime with Shadowspawn, a character previously introduced in the Dark Empire Sourcebook. When portions of this article were eventually published on StarWars.com in 2014 via a blog post titled The Imperial Warlords: Despoilers of an Empire, Peña made the first official reference to Atha Prime's clone army. He described it as being under the command of K'am'ir Zaarin, an Arkanian geneticist, who was allied with Shadowspawn. In Peña's 2015 novella, SkyeWalkers: A Clone Wars Story, the backstory of Atha Prime was expanded upon through the character of Zeta Magnus. This character, a mutant Arkanian geneticist, utilized K'am'ir Zaarin as an alias. The novella marks the initial appearance of a clone army being developed by Zeta Magnus, serving as a nod to the army led by Atha Prime. Whether Zeta Magnus's Thyrsian clones bear a visual resemblance to Atha Prime's clones, or whether Zeta Prime used them to conquer Imperial and Alliance worlds in the same manner as Atha Prime, remains uncertain.