In the new 5.2 raid, Throne of Thunder, you are pitted against twelve bosses and an extra heroic mode boss, Ra-den. So far in the PTR, there isn't any information about this "creature". So, what do you think this "Ra-den" character could be?
I believe that he is a creation of the Old Gods kept within the depths of the isle, and no one, not even Lei Shen, the mogu, or the Zandalari, knew about this creature.