Na-Krul is the main antagonist of Diablo: Hellfire, the first expansion of the original Diablo game - he was once an agent of Diablo but was cast into the abyss by his former master under unknown circumstances and later summoned to Earth by a foolish sorcerer who he ultimately killed.

Na-Krul began unleashing hordes of new and powerful demons into the world while making a crypt his stronghold, eventually he is fought as the final boss - with Ka-Krul's defeat his hordes presumably perish and the world is given some relief from demonic invasion (at least until Diablo II that is).