Thalamus

[Aeternalis the Abyssal Alchemist]

My thoughts on the boss:
It kind of reminded me of mix between Photoshop Flowey(Undertale) and Delirium(Binding of Isaac). I like the boss' physical design and premise, the fight is a bit lackluster though.

What's the deal with Thalamus anyway? I feel like his existence is supposed to be more impactful, but none of the characters ever acknowledge him, even though his voice is still heard at points well after 'defeating' him, often taunting you. Heck, the title screen even changes after you encounter Thalamus and stays that way. Its like they were planning to more with him, but gave up.

[NK77]

The Eldritch Council is worshiping him, you can see a statue of him in the boss area.
The boss fight change a bit depending on your relationship with some NPCs.
Dunno if there's more. You won't see him if you don't die.

[TheQuestion]

Fear is always present, without it you are dead.

[Z柳]

towards the end of the game, you can actually see Thalamus before u fight Endless. in the save statue look up with your mouse.

[Fox Raving Mad]

I'm glad you asked this question, I assumed he was an alternate final boss fight after the last boss. I also assumed there would be some dialouge between you and death about em. It was a cool boss, alot of nifty things but... Yeah. I too would like a small lore dump for him.

[khangkhanh]

He's optional if you cancel the Death Contract. Basically because you fear "death", you keep the contract to keep yourself alive. He exploits that to torment/kill you over again like Flowey. The whole area was his creation.