Koz Koroja

The Heartrender

Koz Koroja is a pit fiend general in the service of the Arch Duke Dispater.  
Recently, an agent of his (known as the Melody) was slain on the Material Plane under the city of Damarask.  The exact reasons for Koz Koroja's interest in the realm of mortals is still unknown, although some recent clues have been discovered.
According to the Melody's journal, Koz Koroja is using corrupted souls to power a device called The Heartrender's Key.  This device, whatever it is, will be used somewhere called The Ruined City when the time is right.