Deathwing had not always been called Deathwing. In fact, that name, which hardly sounded like it belonged to anyone good, did not suit the commander of the Black Dragonflight. He had once been called Neltharion, and among the first generation of the Dragonflights, he had been a highly respected figure.
That was mainly because, in the battle against the monstrous Galakrond, Deathwing had appeared as a courageous warrior. Of the five Dragon Aspects, only he had dared to confront Galakrond, a hundred times his size, head-on-and he had held his own.
That alone showed how powerful Deathwing's body was. Later, when Tyr recommended the dragons to the Titans as the world's Watchers, Neltharion also caught the eye of Khaz'goroth, the Pantheon's Earth-Shaper. Through the Shaper Archaedas, he was granted dominion over the earth of Azeroth.
From then on, the age of the Guardians ended, and the age of dragons began.
Yet even the wisest of them, Nozdormu the Time-Lord, could not say when his brother Neltharion's corruption had begun. The only certainty was that, over his long years of maintaining the earth's balance, Neltharion had heard voices that should never have been heard in the darkness deep underground.
And it seemed there had been more than one Old God.
Corrupting a Dragon Aspect while imprisoned was far beyond what a single Old God could accomplish. Thus, to those familiar with that history, Neltharion's corruption and Deathwing's emergence had very likely marked the beginning of all the resistance and dark schemes jointly undertaken by three Old Gods.
In short, the earthen power granted by Khaz'goroth had given Deathwing the strongest head-on offensive power of all the Dragon Aspects, while also making him the most likely to come into contact with that darkness.
As Alexstrasza, the Red Dragon Queen, so often said,