This may be the first question asked of the audience via the title. Who is this guy? Who's this true detective? Is this a reference to some lurid tabloid filled with fiction disguised as true crime stories? Is it an actual person?
In tracking down some answers to this question, I was able to outline some of the key differences between Cohle and Hart; some of the subtleties of the relationships among the cops in the squad room, the citizens of south Louisiana, and the criminals; the policeman/investigator/gumshoe triangle; the different kinds of gumshoes that Cohle and Hart each represent; and the ultimate nature of Hart and Cohle as Janus figures.
Not bad for a few notes.
Hart is the police procedural guy. If you need someone to do footwork, to interview witnesses (which is different from interrogating suspects, please note), to track down documents, to check IRS filings, then he's your guy. He's patient, methodical, focused, clear, and insightful. He's resourceful and clever. The best example of this is when he tells Cohle how he tracked down the company that did the landscaping on various government properties and how it was linked to another company that the Childress family ran. (As an aside, keep in mind that these kinds of municipal/state contracts are wildly nepotistic in the South, and the deeper you go, the worse they get.)
Hart is a gumshoe without the freedoms of true independence; whereas the gumshoe traditionally does not have a wife, children, or other family ties, Hart's children and to some extent his ex-wife keep him bound to the area. Otherwise, Hart has the classic gumshoe characteristics: he's rough and unrefined; he knows how to work someone over; he's good with details; and he only fits in as a cop when he's with other cops and citizens in the daylight. Once nighttime falls, he becomes someone different.
In contrast, Cohle is an investigator. He's a gumshoe without any need to be a gumshoe. He's rejected, an outsider, dismissed by his colleagues. He's smarter than other cops, more experienced, and because of that, he doesn't fit in well. He can fit in as a police investigator during the day, but as with Hart, he's in his true element in the nighttime scenes. More so than other investigators, Cohle "knows some moves," as Hart puts it, and above all else, he is a supreme "box man" or interrogator. As within the gumshoe tradition, Cohle must contaminate himself with drugs and alcohol (the alcohol disguised as cough syrup) to access the borderlands of criminality. He uses the prostitutes at the truck stop to get drugs so that he can sleep, as well as using them to get information about Dora Lange.
Both Hart and Cohle are Janus figures, dual faced and duplicitous. Hart's infidelities make him overtly duplicitous, but in ways that do not matter to the police force. His duplicities are of no consequence to his colleagues. On the other hand, Cohle seems as if he is concealing everything about himself, yet he conceals very little. He is in no way duplicitous, yet others believe that he is, because to believe him and to believe in him would mean no longer denying that he is superior outside of being a box man. Cohle is ultimately the figure that shows up the lie of equality-as-identicality.
So who is the true detective?
It's too easy to say there's no true detective. Cohle and Hart are compromised as police officers, as investigators, and as persons. But is it possible to be a true detective, and if so, what does it mean to be one? Is there a code by which a true detective may live? What would that code be? The operative word is "true." Is it possible to be true, and if so, what does that mean?