This must be a story known to my generation... ah, probably even to my uncle's generation. For the previous generation, memories like these often involve places like "Internet cafes."
This story comes from a Blizzard Entertainment franchise. In this tale, a magical world is suddenly afflicted by a "Scourge"—a calamity that causes the living to fall ill and die while the dead are resurrected as monsters. The leader of the Scourge is known as the "Lich King."
Many years later, a hero, along with a few companions, made their way to the throne of the Lich King and ended this evil leader. However, at that moment, the spirit of a deceased hero suddenly told the hero that if the Lich King were to die, the Scourge would completely spiral out of control, bringing devastation to all living beings.
Therefore, "there must always be a Lich King."
Sometimes I think that we actually live in a world filled with Undead.
Really, it's not an exaggeration at all.