Although its most direct references to weird fiction are, of course, to Robert W. Chambers and Ambrose Bierce (namely 'Carcosa' and 'The King in Yellow'), it is the spirit of H. P. Lovecraft that most pervasively haunts True Detective. Now, Lovecraft of course appropriates the names 'Carcosa' and 'The King in Yellow' for himself and his own cosmo-mythology, but that's not what I'm talking about here. True Detective is the most purely Lovecraftian thing I've ever seen on television.
The Lovecraftian elements are not arrived at through simple name-dropping, though that certainly helps. Something much more subtle and clever happens in True Detective. It hardly needs to be said that much of Lovecraft's legacy is derived from the new pantheon of monstrosities he gives us, but it should also be remembered that he was far more than a simply pedlar of novel beasts and terrors: what Lovecraft does with great skill is endow the familiar with an otherworldly atmosphere. The very soil beneath our feet becomes infested with entities of unspeakable age and power. Lovecraft is able to warp the world we take for granted into something profoundly different and disturbing. He can twist things, take what you know and turn it inside out, force you to recognise how limited and illusory your understanding of the world is.
On a level of sheer aesthetics, True Detective is certainly able to achieve something like that. It implants the idea in the viewer's mind that behind the ordinary is something abnormal and threatening. As well as that, there is just something about the way TD is shot that makes the landscape, the endless swamps and always-in-the-distance industrial edifices unsettling, and I'm not sure what. It feels as if there is a quintessential element within the environment that just makes it wrong somehow, an element that cannot be easily defined. It's just there.
The show's cosmic pessimism and nihilism is very much worth mentioning here (the ending not withstanding). Cohle does more-or-less literally quote Thomas Ligotti (imagine a more disturbed H. P. Lovecraft, and you've got an idea of what Ligotti is like), who is possibly the most pessimistic writer I've ever come across. One of Lovecraft's most important characteristics is that his monsters are not 'evil' as such, they generally don't hold any direct malice towards humanity: they're just indifferent towards us, utterly so. To them, we're prey, or a nuisance, or occasionally entertaining playthings- but they are so far beyond us, so different, so purely alien that their motives cannot be grasped, and using words like 'good' and 'evil' to describe them is as absurd as calling the sun 'cruel' for giving you skin cancer. Cohle is a character who has grasped the uncaring nature of the universe, the absence of purpose, of grand narratives, of moral absolutes. That is where much of Lovecraft's horror lies: Cthulhu doesn't want to drive you mad, he just will.
These broad thematic strokes aside, the two most direct nods towards Lovecraft are somewhat blended together: the heavy hints at degenerate heredity and atavism, and the presence of a cult. The show is littered with references to Devil worship in the woods, of peculiar blends of Voodoo and folk-religion (and the use of mainstream religion to mask dark esotericism), culminating in Cohle's encounter with the bizarre and never-explained idol of The King in Yellow in the equally bizarre and unexplained Carcosa. Exactly what is it that motivates the killings? How does Childress have such a powerful affect on people? Why is any of this happening? At the end of the show, all we have are a few culprits, a few bad people who were doing bad things: but their motivations are never explained, not even remotely. It is obvious that a substantial conspiracy, going all the way up to high-office, is involved throughout the State, perpetrating and covering up murder, abduction and child abuse, and although sexual perversity is certainly part of the motivation... that just doesn't feel like the whole story, does it? Something more was going on there, in that house, in those tunnels. Something that cannot be grasped except at the expense of sanity. Cohle certainly glimpses it with his vision of a great vortex in outer space, and the thought of it disturbs Marty sufficiently that he has no desire for the details of what was found there, what that family had been doing there for so long.
It was absolutely the right decision for the show to not tell us why any of this was happening, what these people sort to accomplish with their deeds, if anything. The feeling it leaves behind is that we, the viewers, have been shown a glimpse at a hidden world, one just behind the veil of convention and assumption, containing a presence we simply can't believe exists, and yet is sharpening its claws and eyeing us intently.