Iokath was a massive sphere constructed around a star located in the Iokath system somewhere in the Unknown Regions, specifically Wild Space. This was the origin planet for the GEMINI droids, SCORPIO, the Eternal Fleet and the Gravestone.
Iokath's origins are shrouded in mystery. It was created by an ancient, highly advanced civilization that attempted to create the greatest weapons in the galaxy. To achieve this, they sent their droid armies to randomly-selected planets, where they waged war on the natives, until the Iokathii had got what they wanted. They then offered help rebuilding the worlds they'd destroyed.
Some time after Iokath's construction, however, the Master Designer, the chief engineer, got tired of using their weapons in simulations, and longed for the real battlefield, testing its power on Iokath itself. The armies destroyed the population, despite efforts to strand them in Wild Space and wipe their memories, until it was driven back by the Gravestone, a superweapon which was left on Zakuul after a battle against the Eternal Fleet. By then, the people on Iokath were destroyed and ARIES, a war AI designed to lead simulations, eventually took control over the planet and destroyed anything organic by putting them through impossible "tests" for the supposed goal of determining who would inherit Iokath.
Iokath was rediscovered by 3632 BBY, when SCORPIO, determined to discover the origins of both herself and the Eternal Fleet, hijacked the Gravestone and discovered Iokath's location in its databanks, bringing both it and the Eternal Fleet back home. Upon entering the planet, ARIES used a planetary superweapon to render the crews of the fleet insensate, and spread them across the planet for his "tests". However, the leaders of both Alliance and Eternal Empire, the Outlander and Empress Vaylin, led their followers in open defiance of ARIES that the droid was forced to erect a planetary shield around Iokath to prevent their escape and began charging the superweapon to neutralize them permanently. SCORPIO managed to destroy ARIES before he could succeed and shut down the weapon and the shield, but the weapon discharged a massive amount of radiation that flooded the planet, though the Gravestone and the Eternal Fleet managed to flee. The Alliance later sent scouting parties to Iokath, but the radiation levels forced them to wait until the planet was safe to explore.
Battle for Iokath
Following the dissolution of the Eternal Empire and the rise of the Eternal Alliance, Lana Beniko led an expedition to Iokath when its radiation levels finally dissipated. However, both the Galactic Republic and Sith Empire had arrived on the planet as well, seeking to gain control of the superweapon to become the dominant force in the galaxy once again.