The Essence of Zhaal was an artifact that was a component of the evil demigod Vortek, extracted from his body by the demigod Shalde during his defeat. The Essence was placed in a small bottle, resembling a drop of viscous, purple liquid, and later transported to the monarchy in Wolkaea to prevent Vortek's revival. However, the Essence was later collected by the Darkheart and used to reconstitute Vortek, once again becoming part of his mortal form.
The Essence of Zhaal, named after a powerful soul manipulating demon, was capable of twisting the souls of the individuals that consumed it. When ingested, the Essence would temporarily bind itself to the soul of the victim, forcing them to regurgitate it; this soul, in turn, could be bound to the user of the Essence, allowing them to reform the victim's soul however they pleased. However, the artifice of the Essence was that its use would slowly erode the soul of its user, bringing them down to only their base desires and primal instincts.
Originally in the hands of the ruling monarchy of Wolkaea, the Essence was kept secret for many years, guarded by powerful wards and magical safeguards. However, around 810 IaC, one of the kings of Wolkaea grew curious about this treasure that he technically possessed, but could not see. He removed the Essence from its safety and began obsessing over it, discovering its bizarre powers. For years, Wolkaea's political enemies and antagonists would suddenly become ardent supporters of the monarchy, products of the artifact's power. It was eventually was taken by force by the Nightseeker, who began to use it in order to gain greater power for herself.