Actually, according to the warcraft novels, Deathwing is driven insane by the whisperings of the old gods (C'thun and friends) and has a small army of goblin smiths melt hot metal plates into his dragon scales (ouch!)
He then convinces the other dragon aspects to give up a piece of their power, crafts an item called the dragon soul, allowing him to control the other dragonflights, and uses it to wipe out most of the blue dragonflight (and drive Malygos insane in the process)
These overgrown lizards are pretty fragile of mind, come to think of it.