To be honest, there isn't a lot of information on this being except that he is a means to an end. When Iron becomes this devil, that is when you know the end is near.

His feathers will be the only sign left of his arrival..

Those blackened flames that are used in the burning of the land during the apocalypse...

Hot enough to scorch the land and with the feriocity of a dragons rage..

He is the beast..