The Molten Core lies at the very bottom of Blackrock Depths. It is the heart of Blackrock Mountain and the exact spot where, long ago in a desperate bid to turn the tide of the dwarven civil war, Sorcerer-thane Thaurissan summoned the elemental Firelord, Ragnaros, into the world. Though the Firelord is incapable of straying far from the blazing core, it is believed that his elemental minions command the Dark Iron dwarves, who are in the midst of creating armies out of living stone.
The burning lake where Ragnaros lies sleeping acts as a rift connecting to the elemental plane of fire, allowing the malicious elementals to pass through. Chief among Ragnaros' agents is Majordomo Executus - for this cunning humanoid is the only one capable of calling the Firelord from his slumber.