The reason there are two kinds of characters goes back to the concept of the Story Mind. We have two principal views of that mind: the Objective view from the outside looking in, and the Subjective view from the inside looking out. In terms of the Story Mind, the Objective view is like looking at another person, watching his thought processes at work. For an audience experiencing a story, the Objective view is like watching a football game from the stands. All the characters are most easily identified by their functions on the field.
The Subjective view is as if the Story Mind were our own. From this perspective, only two characters are visible: Main and Obstacle. The Main and Obstacle Characters represent the inner conflict of the Story Mind. In fact, we might say a story is of two minds. In real life, we often play our own devil’s advocate, entertaining an alternative view as a means of arriving at the best decision. Similarly, the Story Mind’s alternative views are made tangible through the Main and Obstacle Characters. To the audience of a story, the Main Character experience is as if the audience were actually one of the players on the field. The Obstacle Character is the player who blocks the way.
To summarize then, characters come in two varieties: Objective and Subjective. Objective Characters represent dramatic functions; Subjective Characters represent points of view. When the Main Character point of view is attached to the Protagonist function, the resulting character is commonly thought of as a hero.
From the Dramatica Theory Book