Lord Toruk
This is the uber big grand baddie of the warmachine/hordes universes. While Menoth and the Devouring Wyrm are dicks, at least they are not causing a ruckus in the world like this guy is.
No one knows where Lord Toruk (oh his grand highness likes to be called Lord does he? Well pardon me your Grace) came from and he is not telling anyone. The only thing known is none of the Gods had any involvement in his creation and only they might know his origins.
Growing lonely and fancying some buddies, he split his crystal heart into pieces and created a bunch of dragon children. These ungrateful brats quickly showed just how like daddy they were and all they started fighting each other for dominance.
Since then Toruk's thoughts are bent to consuming his childrens' hearts to make them one with himself again and to do that he created a kingdom of zombie pirates, Cryx (which shows Toruk has some uncommon tastes in minions). He has his minions search for his offspring while also weakening the other nations of the world, so that like a cancer his empire will grow and consume all the lands.
Now the Dragonfather waits patiently, biding his time until he will take flight again and take care of his children once and for all...