The Darker, an entity born from the Arbran people's collective negativity. Around 25,100 BBY, during the era of Xim the Despot, the Arbrans flourished on the planet Arbra. This civilization might have shared ancestry with the ancient Sith, evidenced by the similarities in their respective languages.
The Arbran society progressed to a stage where eliminating negative feelings such as anger, hatred, and fear became a primary goal. They even invented technology to achieve this. However, they lacked the means to completely eradicate these negative energies. Instead, they chose to contain them within a subterranean cavern, sealed off by an energy field. This energy barrier also acted as an impediment to sentients experiencing negative emotions. Over countless years, the trapped emotional energies coalesced into a conscious being, which they named The Darker. Despite possessing the ability to eliminate the creature using the force screen, the Arbrans declined, considering it an intrinsic aspect of themselves.
Eventually, the Arbrans abandoned their original homeworld to rebuild their society elsewhere. The Darker remained confined on Arbra for thousands of years.