Kotharel the Harvester is a radiant idol, a fallen angel cast out from the plane of Syrania. After "harvesting" souls for 23 years, Kotharel was brought down by the knights of Dol Arrah and sentenced to Dreadhold prison.
Once an angel of Syrania, Kotharel was cast out by the host in the year 710 YK and banished to Eberron for all time. There, Kotharel became a self-stylized lord of death called the Harvester, seeing itself as the right hand of the Keeper. In this role, Kotharel inspired a murderous cult who would "harvest" the souls of innocents in its name, sending them to the Keeper.
After 23 years of this, in the year 733 YK, the knights of Dol Arrah tracked Kotharel to Metrol in Cyre. In a battle that rocked the city, the knights defeated Kotharel and its cult, but could not kill the immortal enemy. Thus, the knights brought Kotharel to Dreadhold, an inescapable prison run by House Kundarak. They placed Kotharel in the Deep Ward, a portion of Dreadhold with a permanent anti-magic field. Kotharel sits in Dreadhold to this day.
Kotharel possesses all the abilities of a radiant idol with the Death domain, and much more. It is much stronger than others of his kind but without being any larger. It regenerates all injuries, takes no damage, and even reforms from disintegration; it has no vulnerabilities; and is immune to death magic, making it immortal. Because of his loyalty to the Keeper, any weapon wielded by Kotharel becomes a Keeper's fang.