The book's action takes place around the Texas / Mexico border in the 1850s, and is loosely based on real events (making it that much more disturbing). The protagonist (more or less) is nameless but occasionally referred to as The Kid, a runaway from Tenessee who finds his way into a group of mercenaries headed by John Glanton (a historical figure) and animated by the monstrous and demonic figure of Judge Holden, who like Anton Chigurh in No Country for Old Men is an incarnation of not just death, but of pitiless and absolute nihilism.
The Coen brothers have a very obvious nihilistic streak and it sometimes gets directly incarnated in their films (eg Anton Chigurh in No Country for Old Men or the tornado that appears at the end of A Serious Man – cinematic depictions of the universe's pitiless and antihuman forces of destruction). And of course there are actual literal nihilists in The Big Lebowski, as well as the greatest commentary on nihilism of all time.
I'm haunted by this scene towards the end of this fantastic movie, one of very few I can think of to discuss agency and causality explicitly:
Carla Jean: the coin don't have no say – it's just you.
Chigurh: I got here the same way the coin did.
The enigmatic figure of Chigurh in this movie not only represents the forces of death, he consciously makes himself into a servant of the inhuman and uncaring processes of the physical universe, in its randomness and meaninglessness. He's something of an anti-agent.