In No Country for Old Men, who does Anton Chigurh work for (Why did he kill them?)

Chigurh was called in by the (unseen) ringleader, after the drug deal went bad. His main assignment is to recover the money.

A secondary assignment is to kill the guys who the ringleader had hired to set up the deal that went bad (apparently the ringleader doesn't tolerate screw-ups). But first Chigurh needs their information and their transponders, so he meets with them before killing them. Obviously, they don't realize what's coming.

Chigurh has no regard for who he kills at all. He gambled a shop keepers' life on the flip of a coin. He killed those men because he is indeed a murderous lunatic:

Man Who Hires Wells: I'd just like to know your opinion of him. In general. Just how dangerous is he?
Wells: Compared to what? The bubonic plague? He's bad enough that you called me. He's a psychopathic killer, but so what? There's plenty of them around.

Whether he worked for the white men or not it doesn't matter. He has no regard for anyone's life no matter who it is. Also he may have only been accompanying those men to buy the drugs and maybe he works for their superiors.

But nevertheless, he is simply a psychopathic killer.

The answer is there is an unseen layer in the movie. In the book he kills off the men who set up the botched drug buy, including the man who hired Wells. He then returns the money to the money man who is not shown in the movie. He then sets himself up as the in between man for the money backer.

If memory serves...

Americans are buying drugs from Mexicans, but the deal goes bad. Chigurh is hired by the Americans to retrieve their money. Once he's killed half of Texas, and brought a whole lot of unwanted attention on himself, all while failing to actually retrieve the money, the Americans get scared that Chigurh has gone nuts or may get caught and lead back to them. So they hire Wells to get the money and kill Chigurh. Chigurh does not take kindly to this, and kills the Americans. In the book, there's an extra scene where he then gives the money (minus expenses) to the Mexicans, thus completing the original deal, and announces that he's working for them now.

I don't remember why he kills those first two men - maybe he's been ordered to kill them for setting up a bad deal, maybe he kills them because they've seen his face and he doesn't trust them, or maybe he kills them because he's crazy.

First off, Chigurh used to work with Wells. From the start, Chigurh, due to the deal on the caldera that went bad, several people gave bad advice to the boss arranging the meet. So not only did he need to retrieve the money, but took it upon himself to also eliminate those in fault for setting up a terribly planned trade, thus the killing of the two "managerial lads." During his chase to recover the money from Moss, he is also systematically eliminating those within his organization he thus believes untrustworthy or implicated in setting up a bad trade. At the end of the book, he returns the remaining money to it's owner and informs him things will be run differently. They'll be dealing with new people now.

He works with the two men in the beginning who were all employed by the fat office boss. The one guy called him a Bitch because Chigurh would have been an extra hire (less of a reward). But once they gave Chigurh the locator he figured fuck the bounty. I'll kill these two and keep the two million for myself.