Wikipedia: The psychopath is defined by a continual seeking of psychological gratification in criminal, sexual, or aggressive impulses and the inability to learn from past mistakes. Many psychologists believe that psychopathy falls on a spectrum of pathological narcissism, ranging from narcissistic personality disorder on the low end, malignant narcissism in the middle, and psychopathy on the high end. An almost all-pervasive misconception is that psychopaths are doomed to a life of violence and crime. It is possible for psychopaths to become successful in many lines of work. Psychopathy is frequently mistaken with other similar personality disorders, such as dissocial personality disorder, narcissistic personality disorder, and schizoid personality disorder (as well as others).

Insanity is no longer considered a medical diagnosis but is a legal term in the United States, stemming from its original use in common law.[3] The disorders formerly encompassed by the term covered a wide range of mental disorders now diagnosed as organic brain syndromes, schizophrenia, bipolar disorder and other psychotic disorders. In English, the word "sane" derives from the Latin adjective sanus meaning healthy. The phrase "mens sana in corpore sano" is often translated to mean a "healthy mind in a healthy body". From this perspective, insanity can be considered as poor health of the mind, not necessarily of the brain as an organ (although that can affect mental health), but rather refers to defective function of mental processes such as reasoning.

From studying psychology for two years and college, as short as it was, I honestly can't see the Joker as insane and probably not even a psychopath. He would best be termed as a Sociopath. However Sociopath is no longer used and rather regarded at "Antisocial Personality Disorder". Which completely fits him if you look at the symptoms.
• Persistent lying or stealing (possible, but I don't think he's lying. He believes in what he's doing and wants to prove a point. whats the point in proving a point of no one believes you?)
• Recurring difficulties with the law (gee....um..duh?)
• Tendency to violate the rights and boundaries of others (he kills people merely based off a whim. so yeah...)
• Substance abuse (from everything we've known about the Joker, surprisingly he doesn't to our knowledge. as he says "...and you know the thing they have in common? they're all cheap. its not about money [or in this case drugs] its about sending a message.)
• Aggressive, often violent behavior; prone to getting involved in fights (again, this is obvious)
• A persistent agitated or depressed feeling (dysphoria)
• Inability to tolerate boredom (during the interrogation with batman, and throughout the movie he claimed how he wouldnt go back to ripping off mob dealers. it was all.....boring without batman around.)
• Disregard for the safety of self or others (again...duh)
• A childhood diagnosis of conduct disorders - this is not a symptom but "a history of" (we don't know much of his childhood so no confirmation on this one)
• Lack of remorse, related to hurting others (uh huh...)
• Superficial charm
• Impulsiveness (yep)
• A sense of extreme entitlement (in this case I could say, he's entitled to making his point about everyone being corruptible and a freak like him so he HAS to make a point.)
• Inability to make or keep friends (unless they're like him...then he usually has no problems lol)
• Recklessness, impulsivity
• People with a diagnosis of antisocial personality disorder often experience difficulties with authority figures.
All things considered here, there is one thing he isn't and that is insane. He knows EXACTLY what he's doing. He doesn't have a definite plan because his plan always changes. He "...just do things." He goes along with what comes at him. That's not insanity, its called creativity. I do that all the time. Its not uncommon. And he's also not insane because he is FULLY AWARE.   He KNOWS  hes killing people, he KNOWS  he's creating chaos. Is it really a mental disorder or is it that he simply doesn't care? They have a word for that too and its called Apathy. Apathy is a horrible dangerous thing.

You guys HAVE to keep in mind that as similar as this Joker is to the Joker in the comic books, its not the same Joker. TDK Joker wasn't dumped in a bat of chemicals to screw with him physically and mentally. He has a back story that actually FITS with his so called "sanity" and why he does the things he does. The Joker in the comics could be deemed a sociopath and a pyschopath, but not the TDK Joker. TDK Joker is more sane then the Joker in the comics. He talks about how it doesn't take much to push someone over the edge, and all that they need is the RIGHT  leverage. Everyone is different and everyone has their own tolerance physically and mentally. I too believe that everyone is corruptible. Keeping in mind that corruption can come in MANY forms. Big or small. For myself, mentally and physically I KNOW what its like being on the edge and almost tipping over it. Emotions alone can cause horrible distortions.

Scar Stories: they make sense. When you're a child the world is obviously a different perspective then when you're an adult. You're naive and usually believe A LOT of what you see. Why do you think they always say "young and stupid"? Its because its true. Him being a kid and watching what are SUPPOSED to be your mentor and loving parents turn out to be a horrible nightmare you cant escape from. Imagining a drunken father taking a butcher knife to your mom and then coming at YOU with the knife and sticking it in your mouth? That's a horribly frightening image and there was NOTHING he could do about it because he was a kid.

Then years later he gets a wife. From the telling of his wife story it sounded like they lived in the slums or broken down areas since they didn't have "enough money" to fix her face and the fact she "gambled" and dug in deep with the sharks most likely indicate her attempt at trying to help her and her husband survive with mere necessities. Psychologically, aside from yourself, image watching the one you love deteriorate emotionally and seeing them physically scarred and how it affects them as they slowly dip into negative emotional pits. Its understandable that his wife hit her limit. Not being able to fix your face with surgery means you have to be in public the rest of your life like that. And for a woman....looks sometimes are everything. So imagine how that made HIM feel. So then its ALSO understandable that he would cut up his own face to PROVE A POINT   that he doesn't care about the scars, that he loves her. And its not like he cut his WHOLE face up. Compared to most scars I've seen, his face scars aren't that bad. And then she turns around and LEAVES him? Could you imagine the emotional turmoil that would cause someone? THINK about it.

Because now not only did he lose his only wife and love in his life, NOW his face is scarred with no money to fix it and he is alone to face the world for its cruelty and how people who aren't "pretty" are treated not only socially but in the work place. Its a sad world....ALL of that plus his childhood terrors come tumbling down on him. He just doesn't CARE anymore....nothing matters and so when you have NOTHING   in your life...whats left? And thus....the Joker was born.

Suicidal: What makes him a more dangerous enemy is the fact that he'll purposely put himself into situations to where he could easily be killed...so easy it could be deemed suicidal. His encounter with Batman and the big "HIT ME" scene. Giving Two Face a gun and merely planted it on his forehead and letting chance do the deal. And then finally falling off a high storied building and could have plummeted to his death, laughing all the way, but Batman caught him.
Many would think its just part of his "insanity". But its not insane. Its just apathy...he doesn't care because he has nothing else to loose. But it also goes along for his reasons for using a knife. Quoting him: "You can't save all the little....emotions....." Killing himself would be to easy, just as using a gun would be too easy. What purpose would it serve? What chaos would it provide? However I think he also purposely puts himself in harms way to PROVE to his enemies that he has nothing to loose, that they have nothing to threaten him with.

Joker's Outfit and Makeup
It is a mask, simply like the ones we put on. We all have our own kinds of masks depending on the situation we're in and the people we see. But I think the mask, like Batman's choice of suit, is a symbol. Batman's being a symbol of sharing his fear, something to be feared and respected. For Joker I think it symbolizes his theory of chaos...of BEING an agent of chaos. I mean just look at the details of his entire outfit. Its definitely not ordinary. His socks don't' make sense...the pattern of his shirt is even chaotic in its own way, even if its a simple hexagon pattern. The fact that his entire suit is nicely made and custom, but still wears old shoes that he could easily replace, doesn't really make sense either. Or they're just really comfy shoes lol. His hair...everything about him symbolizes what he represents. And yet still made to the tastes that he likes. So whether the makeup is on or off, he is what he is regardless of how he appears.

I guess like Joker, the bottom line about chaos is that it does....and yet doesn't make sense.

And this all summed up is what makes Joker one of the most well known comic book criminals, and probably one of the deadliest. His psyche alone is complicated and amazing to study and how he pulls things off in the movie are almost...dare I say genius?

Comments by Others on my Analysis
<quote>I do have to disagree with Dracomancer that Joker is not psychopathic. He definitely is in the sense that he's personal goals is what really matters to him and whomever gets hurt in the process doesn't matter. His inability to empathize is very psychopathic in nature. People who are sociopathic aren't as often goal oriented, they live very much in the moment. Any acts that they do that hurt people are done on the spur of the moment, not really planned in advance.

Joker is known for setting up crimes months, even years in advance. That's more psychopathic than sociopathic, imo.</quote>

I was going to retort, but then I realized that I'm no psychologist and what he stated made sense. I still tend to think that, sometimes emotions can make you feel so distorted that simple apathy takes over and you're "normal" emotions get suppressed and you ending loosing the capability of caring about anything anymore other than your goal of doing whatever it is that you're wanting to accomplish from that point on.