There's such an evil presence...

In honor of Tiffany's birthday party (from Wikipedia):

A villain is an "evil" character in a story, whether an historical narrative or, especially, a work of fiction. The villain is the bad guy or heavy, the characters who strive against the hero. A female villain is sometimes called a villainess.

A villain's disposition towards evil distinguishes him from an antagonist. For example, Javert in Les Miserables is an antagonist: He opposes the hero, but does so by such means and under such pretexts as not to become entirely odious to the reader; he may, in fact, even repent, be redeemed, or become a "good guy" in the end. (A villain is virtually always an antagonist, but an antagonist is not always a villain.) The villain is also distinct from the anti-hero, a character who violates the law or the prevailing social standards, but who nevertheless has the audience's sympathy (and may be or become good-hearted,) and is therefore the real hero of the story.
In spite of being the target of the audience's hatred, the villain is an almost inevitable plot device and often – perhaps more than the hero – the central theme of the plot.

The etymology of the word is probably Middle English villein from Old French vilain, in turn from Late Latin villanus, meaning serf or peasant, someone who is bound to the soil of a villa, which is to say, worked on the equivalent of a plantation in late Antiquity, in Italy or Gaul.[1] Consequently, it meant a person of less than knightly status, and so came to mean a person who was not chivalrous; because many unchivalrous acts, such as treachery or rape, are villainous in the modern sense, and because the word was used as a term of abuse, it took on its modern meaning. [2]

The physical attributes of the villain vary according to the culture and epoch, and are often a fairly straightforward reflection of that culture's current prejudices – racial, political, religious, or otherwise. Just as a hero is often a paragon of the prevailing beauty ideal, a villain often has some physical deformity – perhaps to suggest an equally deformed mind (as in the case of Freddy Krueger), or a rough and violent background (as in the case of Peter Pan's Captain Hook or Treasure Island's Long John Silver).

Sometimes even mere violations of the prevailing dress code are enough to label the villain of the story. In fact, the villain is often impeccably dressed, but in a style that deviates somehow from the norm, perhaps only for being too impeccable – like the mafioso in a very expensive suit, or the knight in an overdecorated armor. Another "villain dress-code" would be that of "bad cowboys" and "good cowboys" wearing, respectively, black or white hats.
A typical cartoon villain of the 1970s in American culture is pictured at the top of this article. Note the formal black clothes, exquisitely neat facial hair, sharp facial features, and maniacal demeanour. This cliché was also very common in silent motion pictures, when villains had to look sinister for easy recognition. The Rocky and Bullwinkle characters Boris Badenov, Natasha Fatale, and Snidely Whiplash, as well as the Hanna-Barbera character Dick Dastardly, are well known parodies of this cliché. Sound movies later added to their villain cliché the "evil laughter" and a snooty or smarmy voice.

In opera and musical theater, the villain/villainess is played usually by a baritone/contralto. Overacting is often used by actors portraying the character to stress particular evils.
In many American movies the villain is often British (or implied as such with a stereotypical accent)

While the stereotypical physical attributes may help identify the villain, it is the psychological and moral attributes who make that role. Even harming the hero, or killing his/her beloved ones, will not make a character into a villain – unless it is clear that the act had "evil" motives.
A common psychological feature of the movie villain is a haughty overconfidence that leads to the unnecessary explanation of one's sinister plans – which is sometimes just a plot device used by the author to explain to the audience details which he/she could not express by more natural narrative means. (And of course, those "perfect" sinister plans invariably fail, in part because the villain is too arrogant and overconfident to take any of the precautions described in e.g. the Evil Overlord List.)

Another preeminent feature of the villain's evil character is a tendency to abuse his own accomplices, blame them for his/her own failure, punish them harshly -- even for trivial faults -- and to feel no shame in betraying them should it serve his/her purpose.

Vladimir Propp, in his analysis of the Russian fairy tale, concluded that a fairy tale had only eight dramatis personae, of which one was the villain[3], and his analysis has been widely applied to non-Russian tales. The actions fell into a villain's sphere were
a story-initiating villainy, where the villain caused harm to the hero or his family,
a conflict between the hero and the villain, either a fight or other compeitition
pursuing the hero after he has succeeding in winning the fight or obtaining something from the villain.

None of these acts must necessarily occur in a fairy tale, but when they occurred, the character that performed them was the villain. The villain therefore could appear twice: once in the opening of the story, and a second time as the person sought out by the hero.[4]
When a character performed only these acts, the character was a pure villain. Various villains also perform other functions in a fairy tale; a witch who fought the hero and ran away, which let the hero follow her, was also performing the task of "guidance" and thus acting as a helper. [5]
The functions could also be spread out among several characters. If a dragon acted as villain but was killed by the hero, another character -- such as the dragon's sisters -- might take on the role of villain and pursue the hero.[6]

Two other characters could appear in roles that are villainous in the more general sense. One is the false hero; this character is always villainous, presenting a false claim to be the hero that must be rebuted for the happy ending. [7] Another character, the dispatcher, sends a hero on his quest. This may be an innocent request, to fulfill a legitimate need, but the dispatcher may also, villainously, lie to send a character on a quest in hopes of being rid of him.[8]

Are villains inherently more interesting than the heroes who oppose them? They are at least as indispensable to the stories they appear in, probably more so. Those who stand on the side of righteousness and goodness seldom have much choice but to respond, and little choice in how; for villains, all paths are wide open. Many believe that Satan, for Christians the ultimate villain, is the most interesting character in John Milton's Paradise Lost, for all that he is the embodiment of evil. Perhaps in the nefarious acts of many villains there is more than a hint of wish-fulfilment fantasy, which makes some people identify with them as characters more strongly than they do the heroes. Still, the writer's task in creating a villain is not an easy or a trivial one; a convincing villain must be given a characterization that makes his motive for doing wrong convincing. As put by film critic Roger Ebert: "Each film is only as good as its villain. Since the heroes and the gimmicks tend to repeat from film to film, only a great villain can transform a good try into a triumph."[9]

Villains can be geniuses, (see evil genius), (for example, the highly intelligent Hannibal Lecter), insane (an example being the self-proclaimed Clown Prince of Crime the Joker), power-mad megalomaniacs, (such as the Decepticon leader Megatron, who seeks to rule the universe) dignified (Count Dooku) or all of the above, for instance, Maximillion Pegasus. They may be driven by any number of forces, ranging from greed (Mr. Potter in It's a Wonderful Life and many others, especially criminal) to revenge (Magneto and his vendetta with humanity or Khan and his hatred of Kirk), or even a noble goal twisted by nefarious forces or tragedy (Darth Vader sought power to save his wife, but indirectly killed her instead). Truly, villains are a mixed bag.
However, not all villains are as awe-inspiring as the tall, black-clad Vader or as twisted as the cackling Joker. The character of Man in Bambi was noted as one of the top 100 villains of movie history[10], an impressive feat considering he himself was not completely seen on-screen.

Archenemy – the main and greatest foe of the hero who is the most difficult to defeat; archenemies come with a variety of origins, reasons for their actions etc., although their plots are often threatening to destroy or control a large amount of land, such as the world, galaxy, or universe.
Dark Lord or Evil Overlord – a villain of near-omnipotence in his realm, who seeks to utterly dominate that realm with the help of devoted followers and "Legions of Doom", and whose very name is usually anathema to the lips of the innocent.
Dog heavy – a film term for the third villain in a group, often with minimal or no lines of dialog. The term comes from B-movie Westerns: if the lead villain (or "brain heavy") is the one who leads the group and shoots the sheriff, and the next most villainous kills the deputy, the "dog heavy" is the one who kicks the dog.[11]
Evil genius – a character of great intelligence who chooses to use their knowledge for antisocial/immoral ends.
Femme fatale – a beautiful, seductive but ultimately villainous woman who uses the malign power of her sexuality in order to ensnare the hapless hero into danger.
Heel – the villain in a match of professional wrestling
Mad scientist – a scientist-villain or villain-scientist
Supervillain – a villain who displays special powers, skills or equipment powerful enough to be a typically serious challenge to a superhero.
Black Knight – A villain who is noble but is evil through circumstances.
Second string villain – often not very evil or even competent. Typically more ridiculous or annoying than fearsome or deadly and often serve as comic relief. Sometimes they reform and become probationary heroes or sidekicks. Frequently seen as the adult villains in children's adventure stories.
Tragic villain – is a villain who really does not intend to be a "villain" and perhaps believes they are honestly doing good. They are perhaps misled or not entirely in control of their feelings and/or actions.
Antihero – A character who is neither evil nor good, although this type of character is mostly willing to work for either side depending on the circumstances.