Frostmourne

I

Forged in Torghast

For years, Warcraft gave Frostmourne different makers. Warcraft III said it was forged by the Lich King. Later, Arthas: Rise of the Lich King credited the nathrezim, the dreadlords of the Burning Legion.

Shadowlands revealed the real origin. Frostmourne and the Helm of Domination were crafted in the Runecarver's Oubliette in Torghast. Their maker was the Runecarver, who was actually the imprisoned Primus, and he made them against his will for the Jailer. The Jailer wanted the two "vessels of Domination" to spread his influence on Azeroth and get him closer to his "final prize", a secret hidden by the First Ones. Frostmourne was the finest mourneblade the Runecarver ever made, and its runes carried the power of the Maw.

The dreadlords then carried both artifacts across the veil. They were pretending to serve Kil'jaeden all along.

II

Thrust From the Frozen Throne

After Ner'zhul tried to flee Draenor, Kil'jaeden tore apart the old orc shaman's body and kept his spirit. He sealed it in ice from the Twisting Nether and turned it into the Lich King. That icy prison was sent to Northrend with the Helm and Frostmourne bound to it, and it became the Frozen Throne.

Ner'zhul hated being the Legion's pawn. To escape, he pushed Frostmourne out through the ice of his prison and into a cave, where it would wait for a champion. In The Frozen Throne he says it himself: "I thrust it from the ice so that it would find its way to you... and then lead you to me." That act left a crack in the Throne, and his power later leaked out through it.

III

The Inscription

Prince Arthas came to Northrend hunting the dreadlord Mal'Ganis. There he met his old teacher Muradin Bronzebeard, Magni's brother, who had come to find a runeblade said to lie beyond an ancient way gate. According to Chronicle Volume 3, the dreadlords had led the dwarves there by leaving clues about the sword.

A Guardian and its revenants defended the blade and tried to warn Arthas off. He destroyed them. At the dais, Muradin read the inscription:

"Whomsoever takes up this blade shall wield power eternal. Just as the blade rends flesh, so must power scar the spirit."

Muradin understood at once. "Oh, I should've known. The blade is cursed! Let's get the hell out of here!"

Arthas answered: "I would gladly bear any curse to save my homeland." Muradin begged him to leave it and lead his men home. Arthas replied, "Damn the men! Nothing shall prevent me from having my revenge, old friend. Not even you."

At those words the ice shattered, and a shard struck Muradin. Arthas dropped his paladin hammer, Light's Vengeance, and tried to heal him. Then the Lich King started whispering through the sword. Arthas left the dwarf for dead and took Frostmourne.

IV

A King Dies Kneeling

With the sword in hand, Arthas destroyed Mal'Ganis's base and killed the dreadlord. Then he slaughtered his own army and brought them back as undead, and sailed home a hero.

Capital City threw a festival. Arthas knelt before his father, King Terenas Menethil II, then rose and walked to the throne. Terenas's last words were "What is this? What are you doing, my son?" Arthas drove Frostmourne through his heart. A reign of fifty years ended, and so did the kingdom of Lordaeron.

Later the dreadlord Tichondrius congratulated him and revealed the truth: "The runeblade that you carry was forged by the Lich King and empowered to steal souls. Yours was the first one it claimed." Arthas answered: "Then I'll make do without one."

Frostmourne went on to kill Uther the Lightbringer near Andorhal and Archmage Antonidas in Dalaran.

V

Now We Are One

When Illidan's spell widened the crack in the Frozen Throne, Ner'zhul called Arthas back to Northrend. Arthas cut Illidan down at the doors of Icecrown and climbed the spire. With Frostmourne he shattered the icy prison. Then he put on the Helm of Domination, and the two spirits spoke as one: "Now... we are one!" Arthas, the sword and the throne became the Lich King.

Years later, during the war in Northrend, the blade claimed one of the Horde's finest orcs. At the Wrathgate, the Lich King cut down Dranosh Saurfang, son of Varok Saurfang, with Frostmourne. Arthas raised him as a death knight, and later the Horde would face him as Deathbringer Saurfang inside Icecrown Citadel.

VI

Thousands of Souls

According to Terenas's spirit, the blade held thousands of souls. Shadowlands added a darker detail. As a mourneblade, Frostmourne could shatter a soul when it struck in rage. The blade kept a fragment and the rest of the soul went on to the Shadowlands, broken.

Terenas, Uther, Antonidas and the frost wyrm Sapphiron are among the shattered.

Inside Icecrown, adventurers found Frostmourne left unattended in the Halls of Reflection. When Jaina (or Sylvanas) reached into it, the spirit of Uther answered. He warned that the Lich King saw everything the sword saw, and that once the Lich King died, someone would have to take his place.

VII

Shattered by the Ashbringer

On top of the Frozen Throne, the Lich King froze Tirion Fordring in ice and killed every champion who came with him. He started to raise them as his new elite. Tirion called on the Light one last time, broke free, and shattered Frostmourne with the Ashbringer.

The trapped souls poured out and swarmed their jailer, holding him up in the air. Terenas's spirit brought the fallen champions back to life, and they finished the Lich King. Terenas then held his dying son and told him: "No king rules forever, my son."

Terenas warned Tirion that there must always be a Lich King. Bolvar Fordragon took the Helm and the Throne in his place.

VIII

The Shards and the Remnants

At first nobody knew where the pieces went. At BlizzCon 2011, Blizzard said "someone smart" had taken them "somewhere safe".

In Legion, Bolvar, now the Lich King, sent a frost death knight to gather the shards. The death knight had to defeat the echoes of Arthas and Ner'zhul still lingering inside. Then the shards were reforged into twin runeblades, Frostreaper and Icebringer, called the Blades of the Fallen Prince. Muradin was furious when he saw them: "I warned Arthas not to touch Frostmourne, and now I'm warning you: cast those things into the sea before they damn us all."

Shadowlands closed the circle. When Frostmourne broke, the soul fragments it held went straight to the Maw. The Jailer kept them in Torghast's Ossuary of the Banished, as crystals with names like "The Betrayed Father" (Terenas) and "The First Paladin" (Uther). The Maw Walker recovered Uther's piece so that he could heal. The Jailer also had Anduin's sword Shalamayne reforged into Kingsmourne, a mourneblade even stronger than Frostmourne, with a crystal forged from Arthas's soul at its core. When Anduin broke free and split the blade, what was left of Arthas's fading soul was released.