- “Whomsoever takes up this blade shall wield power eternal. Just as the blade rends flesh, so must power scar the spirit.”
- —The inscription on Frostmourne’s pedestal
Frostmourne was the runeblade that Ner’zhul, the Lich King, thrust from the Frozen Throne, intending that Arthas Menethil — his unwitting potential host — would discover it on the continent of Northrend. It was wielded by Arthas, the new Lich King, until it was destroyed following his defeat in Icecrown Citadel. No one knows where the remnants of Frostmourne are now.
When Ner’zhul was transformed into the Lich King by Kil’jaeden, his disembodied spirit was shackled to a magical suit of armor as well as the runeblade Frostmourne, and trapped within an icy tomb called the Frozen Throne. Both the armor and the blade were crafted by the Nathrezim for the purpose of containing and controlling the Lich King.
Ner’zhul’s Plan to Escape
Ner’zhul was not content with being a pawn for the Burning Legion, however, and began working on a plan for escape. The first stage of his plan was set in motion when he used his powers to push Frostmourne through the ice and out of the Frozen Throne, and plunge it into the snows of Northrend to await one who would claim it and become the Lich King’s agent. Ner’zhul found his agent in Arthas Menethil, the young prince of Lordaeron who had come to Northrend in a quest to end theplague.
Muradin Bronzebeard, a dwarven explorer based at the time in Northrend, was searching for the weapon after hearing of Frostmourne’s power when Arthas and his men arrived. When the forces of the dreadlord Mal’Ganis began to close in around them, Arthas and Muradin set out to claim it.
Deep within a hidden, unnamed cave, Frostmourne was guarded by The Guardian and several revenants who tried to warn Arthas of the danger, but he ignored the warning and destroyed them. When they found the sword, Muradin read the inscription on the dais:
Muradin realized then that the blade was cursed, but Arthas said he would gladly bear any curse to save his homeland. Upon speaking those words, the ice encasing the sword shattered and exploded outward. A jagged shard struck Muradin, seeming to strike him down. Arthas, ignoring the loss of his friend, discarded his hammer, [Light’s Vengeance], and took hold of the blade.
In the Hands of Arthas
With the sword in hand, Arthas returned to his base and staged a counterattack against Mal’Ganis, quickly destroying the dreadlord’s base. Mal’Ganis confronted Arthas, telling him that Ner’zhul had known he would take the cursed sword, and that it had now stolen Arthas’s soul. He spoke as if he believed Arthas was now on his side, but to his surprise Arthas used the runeblade to slay the dreadlord on the Lich King’s command. With his soul forfeited to the Lich King, Arthas ran off into the frozen wastes of Northrend.
Now a death knight of the Scourge, Arthas killed and converted his former army before returning to Lordaeron, where he was hailed with a royal welcome. Arthas proceeded directly to the throne room, where he killed his father, King Terenas, and set the Scourge loose throughout the city.
Some time after the Burning Legion’s defeat at Mount Hyjal, the demon hunter Illidan Stormrage used a powerful spell to attack the Frozen Throne, where the Lich King was imprisoned. Though the spell was unsuccessful, it widened the crack through which Frostmourne had been thrust, and the Lich King’s power began to wane, so he recalled Arthas to Northrend to aid him. Arthas defeated Illidan and ascended the spire to the Frozen Throne. He then used Frostmourne to shatter the ice, donned the helmet that was sealed within, and became the new Lich King.
Wrath of the Lich King
The Frozen Halls
Just after he is defeated in the Pit of Saron, the undead gnome Krick lets it slip that Arthas leaves Frostmourne unattended in the Halls of Reflection, his private sanctum in the Frozen Halls of Icecrown Citadel.
After surviving the Pit of Saron, the guides for the adventurers braving the Halls (Jaina Proudmoore for the Alliance or Sylvanas Windrunner for the Horde) lead the way into the Halls of Reflection. As Krick promised, Frostmourne stands alone, floating serenely above an altar in the center of the entry chamber. Jaina or Sylvanas attempt to commune with the souls trapped within the blade to find the key to the Lich King’s weakness. They are contacted by the spirit of Uther the Lightbringer, who warns them that another must take the Lich King’s place in order to keep the Scourge under control.
Fall of the Lich King
During the final battle against the Lich King at the Frozen Throne, Frostmourne was shattered by Ashbringer, wielded by Tirion Fordring. The thousands of souls trapped within the blade swarmed the Lich King, suspending him in the air, where he was finished off by the champions assembled to defeat him.
At Blizzcon 2011, it was stated that the shards of Frostmourne were taken by “someone smart” and put “somewhere safe”… at least until someone gets it in their head to try to reforge it.