Or Amaranth Actual.

So let's go.

My first thought was Dagoth Ur, as he is connected with dreams, dreamers, and was named the dream-sleeved inversion. But he is just a pawn of the Aggregate. So... maybe the Aggregate himself? Aggregate of what? Or who? Was it dwemeri or their golden souls? Or, in that case, Anumidum? Or Princes of Tumult? Or maybe the Eight?

And at this point I thought of "et'Ada, Eight Aedra, Eat the Dreamer", one of my favourites. Could it possibly be that Eight Aedra themselves were the thieves who stole the Dream from the previous Dreamer? And how could that happened?

Now I think about the immortal jellyfish, with eigth limbs (and their missing ninth), floating in the Void, hallucinating, everlasting...