so it seems there's a bunch of people who have approached this show as a whodunnit from the beginning. That's totally fine, and frankly expected. Most of modern fiction and definitely modern television has groomed audiences with the addicting satisfaction of the whodunnit. For those of us who have read the works of H.P Lovecraft and other similar off-beat writers across a range of media recognize a lot of what we love in True Detective. The Yellow King is a "character" that has been passed down and built on by many authors, essentially it is a monstrous cosmic god that exists in the same pantheon as other beings of the Cthulhu Mythos (those unfamiliar look it up). Someone put it really well when they described the Louisiana cult as remnants of a far more nefarious organization, so the killer is essentially an inbred distilment of what the cult once was, however he plays against type as shown by his eccentric display at his house, he's the broken sad end of a once horrific institution, but theres still a fire behind that flabby surface. You can see that fire in the ruins of "Carcossa" and experience his true form as the disembodied voice of the last embers of the cult. Something strange that most people have not talked much about, is the "hallucination" Rust has before getting attacked. The sculpture with the tattered yellow robes and skulls is an avatar of the Yellow King, an effigy. That cosmic spinning maw coming from the infinite reaches of a deep dark space is the Yellow King itself, something elemental, old, and infinitely evil. It is a being that comes from the darkness that Marty mentions at the end, the dark that was before us and seems to be all around us. Rust being close to the madness can see beyond the wall of sanity, and in that instance perceives the cosmic deity. It is this entity and others like it that he refers to in his nearly deranged monologue to the detectives of those who exist outside of time and see it as a flat circle. This isn't why the show is as wonderful as it is, but it's certainly a great layer. For those skeptical, there's a reason why no one googled what the "Yellow King" was in the show. Two detectives would follow up such an important lead and find all the mythology surrounding it, from that you can draw the conclusion that Rust, Marty, and their world exist in the same space as the Mythos, and specifically, that of the Yellow King, who is also known as Hastur the Unspeakable, connected to Carcossa, and the lake Hali. It is Rust coming face to face with the deep dark and his near death that allows him to perceive something beyond the oldest darkness, something underlying it and existing completely beyond and within it, the all encompassing, deeply moving, warmth of Love.