Thalhkarsh was a powerful demon of the Abyssal Planes who was summoned by mistake. The magician who brought him intended to summon an imp called Talhkarsh. He was unprepared for the demon. His summoning circle was insufficient to bind a vastly more powerful creature than the imp he had intended. Thalhkarsh, tortured and ate him. In need of a human chief servant, Thalhkarsh took on the magician's apprentice.
Unlinke other creatures of the Abyssal Planes, who resent being summoned and just want to go home, Thalhkarsh loved the mortal plane. He wanted to remain and rule forever. Thalhkarsh set himself up as a god in the trade city of Delton. The magician's apprentice became his high priest who led his acolytes, mostly the sons of minor nobility, in the "Rites of Dark Desires." As part of this, numerous women were sacrificed to increase Thalhkarsh's power. His goal was to eventually attain actual godhood, so he could remain on this plane forever.
After a hard fought battle, Tarma, Kethry and Warrl killed the high priest and managed to banish Thalhkarsh back to the Abyssal Planes, making their reputation as demon-slayers and champion fighters. Unfortunately, he didn't remain there long. While looking to remove a curse set on him by Kethry, the bandit chief Lastel Longknife hired a failed magician to help him. Not being powerful enough to remove the curse, the magician summoned a powerful enemy of Kethry to do the work. What he got was Thalhkarsh. The demon killed him, captured and transformed Lastel, and set himself on the road to godhood once again.
He took over the abandoned temple of a rain god located in the poorest quarter of the city of Oberdorn. This time he fed on the deaths of animals in a neighboring slaughterhouse, rather than derive his power from killing women. This kept Tarma and Kethry from noticing he was around again until it was too late. Using Lastel, he captured the women and Warrl. They managed to escape, and with the help of Nemor, the archpriest of Anathei, they defeat Thalhkarsh again. Nemor insured that Thalhkarsh's broken transformation spells would rebound back on him, leaving the demon trapped in the body of a delicate young woman. Still in shock from this sudden reversal, Thalhkarsh's magic was bound by the priests of Anathei who imprisoned her until she accepts the immorality of her actions.