World of Warcraft Lore: Who is Deathwing?

I. CREATION

In the beginning the titans created the leaders of the dragons races of Azeroth. These dragon leaders are known as the five dragon aspects. The dragon aspects were created using Galakrond, a massive proto-dragon that is the ancestor of all dragonkind. The remains of Galakrond can be visited in Dragonblight at Galakrond's Rest.

The titans created these five dragons to watch over Azeroth. Alexstrasza the red dragon in charge of protecting life. Nozdormu the bronze dragon in charge of protecting time and fate. Ysera the green dragon in charge of protecting the Emerald Dream. Malygos the blue dragon in charge of protecting magic. Neltharion the black dragon in charge of protecting the land.

II. CORRUPTION

Neltharion was driven mad by the voices of Old Gods who had convinced him that he could have power beyond his wildest dreams. Neltharion then created an object of incredible power using his own essence to fight the Burning Legion, the Dragon Soul. The voices of the Old Gods then convinced Neltharion that he could take control of all the dragon races of Azeroth using the Dragon Soul.

Neltharion brought the Dragon Soul to the four other dragon aspects to unveil the Dragon Soul. He persuaded them to give their essence to the Dragon Soul. Neltharion used the enhanced power of the Dragon Soul to combat the Burning Legion and began to demand all dragons of Azeroth bow before him. The black dragon, Neltharion fought and killed numerous dragons that stood against him, however he was ultimately unsuccessful and was forced to retreat from the battle.

Due to the corruption that surged through Neltharion from the Dragon Soul,  he was forced to apply adamantium plates to his body to prevent himself from being torn apart. In time the Dragon Soul became known across Azeroth as the Demon Soul and Neltharion became known as Deathwing.

The Demon Soul was eventually stolen from Deathwing by Malfurion Stormrage but was unable to hold onto it for long. Illidan had managed to take the artifact. After Malfurion and the four aspects took back control of the Demon Soul they placed a spell on it preventing Deathwing from using its power and hid it.

III. THE SECOND WAR

Ten thousand years later, Deathwing led the Dragonmaw Clan to the Demon Soul. They used its power to capture Alexstrasza and control the red dragonflight to fight for the Horde. Meanwhile Deathwing disguises himself as Lord Prestor and gains strong influence in the Alliance by befriending King Terenas Menethil II. After infiltrating the Alliance he planned to have the Alliance turn on the Kirin Tor of Dalaran and attack them. A member of the senior council of Dalaran named Krasus had discovered the secret identity of Lord Prestor to be Deathwing and gained knowledge of his plans. He sent his student Rhonin to obtain the aid from the three other aspects to help free Alexstrasza.

Rhonin while on his mission was decieved by Deathwing and was convinced to take one of his scales to Grim Batol. The four aspects fought against Deathwing and Rhonin used the scale he was given to cut the Demon Soul which returned power back to the aspects.

IV. RETURN

Deathwing remained hidden deep beneath Azeroth in Deepholm while the Twilights Hammer created new armor using elementium for him. Eventually bursting through the ground, Deathwing appeared and reigned down fire upon Azeroth. He now currently resides in Grim Batol.