Neltharion the Earth-Warder was the leader and aspect of the black dragonflight Aspect of Earth and one of the five Dragon Aspects, beings empowered by the titans to be the immortal guardians of Azeroth after defeating Father of Dragons Galakrond. However, driven insane by the Old Gods, Neltharion turned on his siblings during the War of the Ancients. Neltharion's body cracked open, revealing his molten heart, and magma and fire flowed off his chest. Goblin smiths forged an armor to serve as a vessel to contain Deathwing's raging powers and keep them in check, which were then placed on his body. Only those plates kept his power from destroying his body. After this, he took a new name - Deathwing, the Destroyer and Aspect of Death. Deathwing was the most powerful servant of the Old Gods, and acted as their instrument of destruction. He manipulated both the Horde and Alliance during the Second War, but was ultimately defeated. He was not killed however, and retreated to the elemental plane Deepholm to recover.
Years later, Deathwing emerged from his realm, outfitted with Elementium plating that barely held his crumbling form together. He began the Cataclysm, an event that nearly tore Azeroth apart. His ultimate goal was to begin the Hour of Twilight, an apocalypse where all life would end and the Old Gods would awaken once more.