Many stories depend upon conflict, and a conflict can only be as intense as those involved in it are closely matched. As such, the opposition to the focal character or characters of a story is every bit as important to that story as those focal characters. That opposition is labeled as an antagonist, but it is not necessarily true that the opposition is evil or even targeted at the focal character or characters. Anything that impedes the ability of the focal character or characters to pursue the end goal of a story is an antagonist. Some examples of antagonists are rabid wolves, muggers on the streets, and overly rigid legal structures.
Wolves often figure as creatures associated with evil; werewolves are classic movie monsters and beasts of folklore, wolves themselves are one of the traditional forms assumed by vampires, and the animals themselves factor in as the villains of such traditional stories as “Little Red Riding Hood.” More concretely, they do present themselves as problems for those whose livelihoods depend upon livestock; wolves prey upon such creatures as sheep and goats, and those who herd them for their living tend to view their predators as enemies. When the already-oppositional lupine is infected with a disease that drives it to unusually aggressive behavior, the antagonistic tendencies of the beasts are only enhanced; rather than attacking sheep, they will attack people, and they are even more insidious in that they can prove fatal from even a minor bite, rather than the severe injuries normally required to kill. The reports of objectionable wolf behavior come from the people who are affected, and as it is a commonplace for the tellers of tales to present themselves as the focal characters or to speak on their behalf, the rabid wolves find themselves as the antagonists of the stories told of them. This occurs despite the fact that as animals—and as animals whose brains are affected by disease—they lack the capacity for moral judgment that can actually cause evil, so that while opposition is required for antagonism, direct malevolence is not.
Back-alley muggers, however, are directly and deliberately aligned against those whom they oppose. Attacking victims from ambush and using threats of force or actual force to extract from them what valuables they may have are certainly oppositional to those victims, and since the prevailing social mores maintain that persons have the right to be secure in their own persons, the victims, being wronged, are made the focal characters of the true stories of their being mugged. Also, attacking another person from ambush requires advanced thought and deliberation to establish a position from which to attack and a route from which to escape from the scene of the attack; intent is thus necessary, and is pursued at length by muggers. Opposition can therefore be deliberate, so that those who pursue it are made antagonists.
Both rabid wolves and muggers are discrete, identifiable beings. They can be seen and, potentially, avoided. It is not necessarily true, however, that opposition comes from a directly identifiable being. An inflexible legal system can prove oppositional, even to those who intend no wrong and simply try to live their lives well, and there is no specific person or tangible object that presents that opposition. While it is true that laws are put into place, enforced, and interpreted by individuals, working singly or in concert, the laws themselves are not tangible. There is no single object that is, in fact, the law; destroying no single document or group of documents will actually unmake the law. Even so, it can prove oppositional. Legislation restricting access to certain chemicals—whether used to harm others or by consenting adults in the privacy of their own homes—proves a hindrance to those who would employ them for whatever reason. Legal decisions restricting what can and cannot, and what must and must not, be taught in classrooms inhibits academic freedom and restricts the ability of pupils to learn freely, both of which are oppositional to the free inquiry upon which an open society theoretically depends; it can hardly be argued that those who are trying to learn are acting ill, and those who are attempting to learn are those from whose perspectives narratives are typically presented, so that those things which oppose them must be called antagonistic. Again, though, the raw definition of antagonism only provides for that opposition; it does not even necessitate a distinct thing to present that opposition.
Whatever form it takes, however concrete or abstract, that which opposes the focal character or characters is the antagonist. There are many varieties of antagonist, just as there are many different stories, and it is in the distinctions among them that they become truly interesting.