“Evil – wherever belief in it is held – tends to be thought of in one of two ways. It is either a force equal to or slightly inferior to an opposing force or, as in Orthodox Christianity, the absence, withdrawal, perversion, or deflection of a universal inclination called ‘good.’ Cosmological narratives usually give it both a body and a name and situate it in a separate dark, turbulent, or alien realm. In the so-called natural world, evil may become manifest through the agency of demons or spirits. Whether such demons take on the imaginal form of beasts or humans (even when their form is not always humanly visible), the consequences of their actions are always encountered in the human sphere; that is, even when evil directs itself against animals or vegetation, it is always with an eye toward disrupting the social order (e.g., husbandry, agriculture) and the dependencies of humankind on these areas of human ecology and economy. At its base, evil is a pernicious threat to human survival above all else, and it is essentially different from death itself. Whereas death is universal, evil is selective.
There are countless representations and personifications of evil across history and religious and cultural systems, just as there are many images of the good and the heroic. These various images are depicted [-p.2] in the narratives of both official and folk religions, mythology and folklore, as well as, even quite recently, in the secular metaphors of political and ideological discourse. In virtually all these narratives, at some point the physical representatives of good and evil become direct, often violent, antagonists. The outcome of their struggle for domination over the moral direction of the community holds a central place in its value system.
Perhaps the most dangerous form that evil takes is the visibly human, since when it is ambulatory and mimetic of the individual, it is difficult to distinguish the evil being from a fellow member of the community. This is especially true if there are no obvious markers, such as a tail and horns, to call attention to its difference. When the average person cannot definitely identify another individual as evil, yet some inexplicable adversity suggests malevolence that has gone beyond mere temper, it is critical that the threatened individual or collective immediately locate evil’s nexus – even if it is found to be the heart of a neighbor and there is no confirming evidence aside from belief. Once evil is found, it must be destroyed or, at the very least, banished far beyond the possibility of return.
In contemporary Western European and North American popular culture, the vampire has become one of the most pervasive and recognizable symbols of insidious evil. Though, according to some notions, the vampire can shift his shape into that of a wolf or bat or other animal and perhaps possesses other supernatural powers, he is different from monstrous beasts or even from Satan in that he possesses a single human body. Furthermore, in both folklore and literature/cinema, in his humanlike, untransformed state, he is not easily recognized as a different order of being. The vampire […] thus has very much in common with the European witch, with one critically important difference: whereas witches are alive at the time they are tortured or ritually executed, vampires are by definition dead or at least undead (whatever that means). But both witches and vampires are held to be evil, for reasons that have much in common.” (pp.1-2)
Ref: Bruce A. McClelland (2006) Slayers and Their Vampires : A Cultural History of Killing the Dead. Ann Arbor, MI, USA: University of Michigan Press