The Voice in the Darkness was an ancient, evil entity that existed in the Milky Way from the beginning of time. It's exact nature is unknown, but it is theorized to have been a C'tan that never placed itself in a necrodermis body or, indeed, interacted with the Necrontyr at all. Whatever its origins, the Voice in the Darkness survived the War in Heaven and continued devouring entire civilizations until it crossed paths with the xel'naga.
The Voice in Darkness despised the xel'naga. The powerful species clashed with the entity, but was unable to truly defeat it. Instead, they used an Argus crystal and the powers of the Void to imprison the entity inside a barren planet which orbited a dead star. The star would one day be designated KL-2.
In 3103 CE, a research team from the Moebius Foundation arrived on that barren world to study xel'naga ruins there. The team was led by a psionically gifted human -- Dr. Morrigan. The Voice reached out to Morrigan, convincing her to create a psionic amplifier for her powers. Under the Voice's influence, she unlocked the creature's prison and unleashed it. Half of her team was possessed by it -- the other half brutally murdered.
Half a sector away, the Dark Templar felt the Voice free itself. A team led by Azimar and Xy'tal arrived on the planet. They were soon assaulted by a converted human -- who, before his death, managed to make psychic contact with both the protoss leaders. The Voice knew of the assault Azimar planned, and sought to bend Xy'tal to his will.
The human minions were cut away by the protoss, until only Morrigan remained. The Voice, speaking through Morrigan, told the protoss it wanted them to be its harbringers. Azimar refused, but the Voice's influence on Xy'tal had grown and he submitted. The two Dark Templar fought, until Xy'tal was able to regain control of himself. He charged an Argus crystal to re-imprison the entity, while the other Dark Templar fled the planet.
When the protoss returned, the planet had been destroyed and all that remained was an asteroid belt around the dead star. The entity had not been destroyed, as it still psychically taunted Azimar -- but its location could not be detected.
Source[]
The Voice in the Darkness is derived from Starcraft.