I think there are 3 types of villains.

The proud ones. Persons who think they have a lot of talents (true or self deluded) and they feel they are repressed by the current system. They do not believe in the current system and turn to other means to achieve their goals. These are usually the final bosses, masterminds and sometimes not really evil.

The outcasts. brutes, violent people who are molded by society, the environment to become what they are. Call a man a dog long enough and don't be surprised if he becomes one. Having a birth defect, being bullied all their lives, not knowing how to fit in society can turn a person into a villain. These are the henchmen, sub bosses.

Loonies. Insane, no real concept of right and wrong. kefka. [grin]

One character that is very difficult to catamlog is Frank Castle, aka The Punisher.

His methods (blow everything and everyone to tiny bits that even FBI's technology won't be able to make out) are not a Hero's. But his goal (get the planet, or at least this country rid of all the wrong doers everywhere) is a hero's. Then how can you define what he is?

By his personal history? His family (wife and daughter) got killed by a mafia gangster while he was on duty. He then turned mad out of anger at any mafia boy, and decided to, in a manner of speaking, "spread the shit as wide as possible. With a shovel if needed."

The methods, the looks, the actions, and the talk, everything in him point to a baddy. But he really is a man trapped in his anger. If you want to create such a character, then create a situation in which anger can be pent up to impossible heights. In ancient japan, the samuraïs knew that when dishonoured or when having lost everything, the rightful path was to disembowel oneself. He chose to disembowel everyone else instead.

Now please consider the path of Peter the Hegemon in Orson Scott Card's Ender saga. He is a child who went mad. In fact, not mad, but merely bad out of interest. He is an extremely brilliant child, with a brain that could figure out space travel course while not out of kindergarden. he got bored, and turned to cruelty towards animals as a passtime, because he wanted to understand the way life works. He was simply completely devoid of moral standards, that being because he could not find anybody to measure himself against. Then came his sister and brother, and he found people he could compete with, but the previous taste for physical violence, and absence of moral standards made him go the mad way. And he became a crazed teenager, believing as hard as his young certainty for being one of the three most intelligent beings on this planet could assert, aiming for world domination through sheer brains. Which he succceeded, through using his sister and brother.

Please bear in mind that every character, be they good or bad, have personal hgistory and motives, and that each should match the other. If you've had a bad personal infancy where you got beaten, you may find it in yourself to become the one who beats the other, in order to stop the fear that you may be beaten again. You may decide to rip the throats of all the people smiling in a particular way around you, because you have a bad memory of someone smirking while you peed in your pants in the middle of kindergarden grounds when three, and the only thing you remember is the smile and the smirk and the tauntings, driving you mad. You may cower before women because you had a mother that abused you when a child, and unleash the brute strength you've built during your life on males, because you don't dare look at women, because they all make you think of your mother, and terrorize you. You are merely trying to show your mother that you have become a strong man not afraid of anything nor of anyone, but you're still a little boy dreading the moment his mother will come nightly in his room completely drunken, and begin to fumble under his sheets, while laughing stupidly.

Remember that most of the extremely violent people have become so because they found this an easy solution to overcome some fear at one point. Those that allow themselves to become soft have never been afraid of anything.

But you might also find the rich and bored and brilliant family son who's got too much time on his hands, and too few real friends to keep him out of trouble? Or the very ambitious mister nobody, who suddendly decides he should kill silently every other people who seeks the same job as himself, in order to keep providing food to his family.

Villains are often desperate to gather either recognition, or fame, or love, or get rid of some fear, and are ready to use just any mean to attain their goal. this is this very lack of moral standards that sets them apart from the heroes...

I think the major difference between a villain and a hero is that villains will stop at nothing to achieve their goals. Anti heroes, while not following the usual rules of good conduct, still have limits which they will not cross. Heroes also take the risk upon themselves to achieve their goals. Villains do not generally take risks and hire other people (which they consider to be disposable) to further their goals.

I considered anakin a villain when he decided to kill innocents to fulfill his goals. And vader became a hero once again when he sacrified himself to kill the emperor.