The Entity Logs, mainly Arcus 54 (Potential spoilers)
So, this log brings a lot of info to the table. If you haven’t read it yet, this is your spoiler warning? Good? Great.
The log gives us a lot of stuff to work with.
1. The Observer can pull anything from the fog through the rift, which makes sense. Secondly, the fog is made of living cells, which also makes sense.
Then he explains the two interesting points, The Entity is something called an Ancient, one of the “Original Ones” whatever that could possibly mean. And there is an entire group devoted to destroying The Entity.
Originally I thought he would be Benedict Baker, but considering Benedict never wanted to destroy the Entity, just solve the mystery of Weeks, that disproved my theory.
then I thought of a small, yet also possible theory. He’s one of the players. As survivors we wish and want our favorite characters to escape and not go into another trial. But, this wouldn’t make complete sense seeing the killer side, people devoted to hunt for the Entity. These players want the Entity to thrive and get rewarded for their deeds. So rule that theory out.
Whomever the Observer is, he is one of the most important characters. He and his “family” as he puts it in game, are devoted to seeking the Entity and destroy the creature, he and his family had theories about the Entity, and he even comments that they were wrong about them. He and his family know a lot about the Entity, and this is extremely invaluable in order to escape the Entity.