In literature, a protagonist and antagonist are archetypal characters that serve as focal points to portray two sides of a conflict. Archetypes are a symbol or motif of a typical example of a thing or person. Differences between the two characters are defined by the roles the two play within a story. Though these roles are often played by two human characters, they can also be represented by elements of nature or two sides of the same character.
In general, the protagonist pursues a solution to the problem presented in the story. Antagonists directly oppose the efforts of protagonists. For example, if the problem is an imminent nuclear reactor meltdown, the protagonist will be pursuing a solution to the crisis, while the antagonist may be trying to cover up faulty engineering that contributed to the crisis. He or she may be attempting to hinder the effort to understand the crisis so it can be resolved.
A narrative is not considered dramatically complete unless there is a conflict between at least two main roles represented within the story, even though there may be only one actor. The two roles may be two sides of a person, or a natural feature or element opposing a person's quest, for example. Regardless of their form, these roles always include the protagonist and antagonist, which are also commonly referred to as the hero and the villain.
People, creatures or elements of nature, like a storm, may fill a role of protagonist and antagonist. In some narratives, the antagonist may be a super-cell thunderstorm, while the protagonist is a scientist who sees the storm coming, but is hindered in his efforts by a naysayer to warn the population. That naysayer may not be the antagonist, but another supporting character in the story. This character plays a dramatic role in which the protagonist is hindered, but not directly opposed.
Protagonist and antagonist roles may also be found in nonfiction narratives. For example, dramatic positioning of main characters may occur in a documentary, in which two scientists debate a controversial topic like global warming. One scientist may be dramatically positioned through editing techniques to be portrayed as the antagonist, while the other is portrayed as the protagonist. Or, both scientists could be filling the protagonist role, while an altered environment may serve the dramatic role of the antagonist that is threatening earth's inhabitants.
The main character often fills the role of either a protagonist or antagonist, but that is not always the case. In general, the main character is the one through which the audience views the story and feels an emotional connection. The obstacle character opposes the main character. For example, one soldier on the battlefield may be the main character through which an entire narrative of an unfolding war is seen. It through his viewpoint that the story of the protagonist and antagonist is revealed.