Zildrog, hailing from Iokath, was an ancient superweapon that, remarkably, became revered as a god on the Wild Space world of Zakuul. Its existence was defined by two permanent forms: a central computer specializing in the conveyance of life energy and the Gravestone, a warship controlled by Zildrog as a part of its own being. Sith Emperor Vitiate employed Zildrog during his infamous Ritual of Nathema, an event where all life on the planet was extinguished and absorbed by Vitiate to achieve immortality, enabling him to reconstruct a remnant of the original Sith Empire into a new empire over centuries. Subsequently, Vitiate deactivated Zildrog, storing it within one of his concealed vaults located on Nathema as a contingency. Over thirteen centuries later, Vinn Atrius and GEMINI 16 discovered and revived Zildrog, intending to harness its power to obliterate the Eternal Alliance. Upon reactivation, Zildrog seized control of the Gravestone, the Alliance's flagship, and unleashed its omnicannon to annihilate the entire Eternal Fleet assembled by the Alliance above Odessen. Before Zildrog could consume the Alliance capital, the Alliance Commander and Lana Beniko launched an assault and destroyed GEMINI 16 on Nathema. Zildrog then imbued Vinn Atrius with power, but this new servant was also defeated, leading to Zildrog's destruction by the Alliance. As its systems failed, Zildrog triggered the Gravestone's self-destruct, resulting in an explosion over Odessen that ended both of Zildrog's forms.
During the Manderon Period, a superweapon of sentience known as Zildrog was forged on Iokath. The Iokath creators, scientists and engineers by trade, constructed weapons of mass destruction to test on unsuspecting planets. Unlike their other mechanical creations, the Six Gods, Zildrog was uniquely designed to exist in two permanent forms: a stationary central computer brain that specialized in the transfer of life energies and the Gravestone, a formidable warship equipped with an omnicannon, which Zildrog could manipulate via the remote command core known as the Dark Sanctuary.
In the distant past, preceding the Great Hyperspace War, Zildrog was deployed on various planets within Wild Space, including a primitive world called Zakuul. Here, survivors began to worship it as a mythical dragon god. Early legends portrayed Zildrog as a mentor to warriors, testing their spiritual fortitude and devouring the defeated. Victorious warriors received the Breath of the Dragon, imbuing their souls with the dragon's fire and promising a bright future. Later, Zakuul also became a target for the Six Gods, who were similarly deified. Eventually, Zildrog merged in perception with Izax, another aerial platform utilizing omnicannon technology. Under the Old Ways, Zildrog was considered a fearsome beast symbolizing death and was seen as one of Izax's many manifestations.
The Iokath civilization eventually destroyed itself in an civil war, which scattered many of its creations across Wild Space, where they were used in local wars. The Gravestone fought the massive Eternal Fleet, another creation of Iokath, and defeated it in a massive battle. After this, it was scuttled in the Endless Swamp on Zakuul, leaving only stories and rumours that no longer associated the warship with Zildrog.
In 4999 BBY, the central computer core of Zildrog was utilized on Medriaas, a fertile agriworld within the original Sith Empire, which had recently collapsed following the Great Hyperspace War against the Galactic Republic. A Sith Lord named Vitiate enacted a potent ritual of Sith magic that bestowed upon him immortality. This was achieved by absorbing the life forces of those killed by Zildrog, empowering himself at the expense of all life on the planet. Medriaas became known as Nathema, and the newly immortal Vitiate deactivated Zildrog, concealing it within a secret vault beneath an ancient Sith Temple.
Vitiate subsequently led the remnants of his people on a twenty-year odyssey from Korriban to Dromund Kaas, where he re-established the Sith Empire in his image. Employing essence transfer to move from one host body to another, Vitiate governed the Sith for centuries, furthering his own objectives. He encountered Zakuul and established a new Eternal Empire on this primitive world, ruling as the Immortal Emperor Valkorion. He proclaimed himself the Demon Savior of Zakuulan prophecy, an immortal god of gods destined to overthrow Izax and the Old Gods, thus ushering in a new era. Over time, the Old Ways faded into obscurity, and Zildrog became known on Zakuul merely as a bedtime story about a creature dwelling in the swamps. Eventually, a nihilistic cult known as the Heralds of Zildrog rose to power, believing that Zildrog would return one day to raze the world, bringing death to all non-believers.
Centuries later, around 3630 BBY, a faction known as the Eternal Alliance toppled the Eternal Empire, and its Commander permanently destroyed Vitiate's spirit. The Gravestone played a key role in the Alliance victory, having been rediscovered on Zakuul and used against the Eternal Fleet, which, after the conflict, came under Alliance control. However, Vinn Atrius, driven by a desire to avenge his people, resolved to dismantle the Alliance. He discovered data from the recently rediscovered Iokath, revealing that the ancient dragon-god of Zakuul was, in fact, a superweapon capable of destroying entire civilizations. Atrius initiated a search for Zildrog and established the Order of Zildrog to further his goals. He received assistance from GEMINI 16, a rogue GEMINI unit that promised to share information on Zildrog in exchange for the destruction of the Eternal Fleet.
After locating a holomap stolen from the Sith Emperor, the Order learned that Zildrog was located on Nathema, and moved to excavate and awaken it. The Alliance discovered their plans and tried to stop them, but by the time the Alliance Commander, Lana Beniko and Theron Shan reached the Temple, the ritual to awaken Zildrog was already underway. GEMINI 16 betrayed some of her allies, locking them inside energy transfer chambers to be used as fuel for Zildrog's awakening, and trapped Alliance members in a force field. Awakened after centuries of slumber, Zildrog demanded a target to feed on, and GEMINI 16 enabled it to connect to the Gravestone, parked on the Alliance capital of Odessen.
Controlling the vessel through the Dark Sanctuary, Zildrog took the Gravestone into Odessen's orbit and proceeded to repeatedly fire the omnicannon at the Eternal Fleet. After the Fleet was completely obliterated, Zildrog targeted Odessen itself but required to gather power before the next attack. This resulted in dropping the force field that kept the Alliance members on Nathema restrained, allowing them to engage GEMINI 16. They fought and destroyed the droid, but before they could shut Zildrog down, Vinn Atrius ordered Zildrog to enhance him with its power. Augmented with increased strength, Atrius attacked the Alliance while Zildrog encouraged his new servant to destroy their enemies. However, the Commander and Beniko defeated Atrius and destroyed Zildrog, which also triggered the self-destruct mechanism of the Gravestone. The warship exploded over Odessen, bringing an end to the era in which Iokath weapons affected the fate of the entire galaxy.
Zildrog was first seen in the Knights of the Fallen Empire expansion of Star Wars: The Old Republic, presented as a deity revered by the ancient people of Zakuul and modern fringe cultists. Zildrog later appeared as the final boss of "The Nathema Conspiracy" flashpoint, released during the Knights of the Eternal Throne expansion cycle. This revealed that it was, in fact, a sentient superweapon originating from Iokath.
During the flashpoint, Zildrog claimed responsibility for the Ritual of Nathema, which caused confusion among players because the ritual was previously believed to be performed solely by Vitiate. Writer Charles Boyd addressed the issue by highlighting player posts that noted the Sith Emperor's ritual always required a mass death triggered by an external source before Vitiate could use the life essences of the dead to empower himself, adding "y'all have it pretty much sorted here".