Frostmourne was the cursed longsword of the Lich King. Lich King Ner’zhul lured prince Arthas to take the blade during the latter’s campaign in Northrend and used it to poison the prince’s thoughts and take hold of his sanity. Arthas eventually betrayed his own people, becoming a Scourge death knight, and continued to wield the blade after he eventually merged with Ner’zhul to become a new the Lich King.
