Kathir is known by many different names. He has been met along the road by weary travelers. He’s supposedly been seen as a man of god in numerous instances. An advisor a thief a mentor. Any guise will suit him fine but the one defining feature in every instance in which he is depicted is that he shall always tempt those that he runs into. He is always seeking to corrupt any and all individuals that he can.
Though many are tempted into terrible fates by Kathir. There are those who especially tickle his fancy. These he hounds until the day of their deaths or until they capitulate and sign a deal with him to be his servants for eternity once they have died. These are the Un-Kathir.
Kathir does not trick anyone. He makes certain that they know exactly what they’re in for. He’s not looking for someone to unwittingly commit an atrocity or corrupt their soul. He wants them to know what their doing and give them the choice so that they willingly choose to violate their fundamental beliefs whatever they may be. His primary goal is to see people voluntarily violate everything they stand for.
Because of this he rarely deals with those who have no scruples. If they are amoral there is nothing for Kathir to bother with and thus he leaves them be. Those he does deal with are forever changed. There is never an encounter where he leaves no mark.