So before The Death Knight King, became who he is know he was an explorer who found a magic amulet that turned him evil. This amulet had a demon trapped inside of it which lead him to the armour set and the battle axe that was to become the stuff he is currently wearing. So after a while this guy started to corrupt some paladins and priest and stuff like that. They became the death knights that follow the King right now and the paladins he didn't convert he killed,he even corrupted the leader of the paladins. After doing this the Death Knight King (or DKK for short) killed the king who was ruling over the land at the time.