We've covered the original game's story, gone to Outland to recap the Burning Crusade, and spent two weeks recapping the events of the Lich King's contumely. Now, we find ourselves facing the dragon that broke the world.
Deathwing's power came in equal measure from the Titans themselves and the Old Gods who opposed them. From the Titan Khaz'goroth Deathwing was granted the role of Aspect of Earth, lord over the land and all beneath it. From the Old Gods imprisoned within the deep earth, Deathwing gained the strength of a kind of madness, a mania with destroying that which he had been set to guard. Rejecting his nature as Aspect of Earth, he would in time dedicate himself to the death of all things living on the surface of Azeroth.
Even before the Lich King's return, Deathwing was taking steps. His prime consort, Sinestra, used the madness of Illidan to cover her own actions, convincing the Dragonmaw chieftain Mor'ghor to give into her keeping a clutch of Netherwing dragon eggs - essentially the eggs of her own descendents, as the Netherwing were born from black dragon eggs Deathwing left behind on Draenor before it was destroyed, exposing the eggs to the raw chaotic magic of the Twisting Nether. In turn, after Sinestra's experiments on the eggs in Grim Batol failed, Deathwing transported a clutch to the Obsidian Sanctim - these dragons were destroyed by the same adventurers who would ultimately kill Malygos. Yet these were hardly the only such eggs warped by Deathwing - a raid on the Ruby Sanctum would reveal that Twilight Dragons now served Deathwing, born from his experiments on the Nether eggs.
All of this was merely preamble. While the situation in Northrend died down following Arthas' death and the secret elevation of the new Lich King, the world had no time to rest. Deathwing had rested in Deepholm since his defeat by the other aspects. Now, he would rest no longer.