As we all know, the Immortal Emperor has outlived the Gods and even kept the Void off for a very long time until we come along and finally put him to rest. However, there are multiple clues that actually implicate that the Emperor has roots going further than that:
Point 1
The Emperor must have known that a Shard exists in the Temple. As a Shard can keep the corruption of the Void back (or at least highly neutralize it), the Emperor must have obviously known of its power and possibly saw his salvation in the shard. This must be the only shard he could get hold of, as the other shards were secured by us, inside the protective ring of the rampant Void. Which leads to…
Point 2
The Emperor could have spent time by the side of Eterra, up to the time when the Epoch got fragmented. While the Gods clearly knew about it, Eterra also had a robed figure chained to a monolith, forever etching into it. It is very much possible that this particular Observer was the Emperor, and he was kept enchained so that he can’t reanimate undead and threaten Eterra’s balance.
Can the Emperor really have his hand deeper than I think?