In Dramatica Story Theory, a Main Character Domain of Psychology indicates an individual who is best described by how he thinks. This could be a flighty person, someone who jumps to conclusions, or even a calculating, manipulative person. In each of these scenarios, the opinions the Main Character holds are not what sets him apart, but rather the kinds of mental processes he goes through. Though there may be many Objective Characters who represent manners of thinking, only the Main Character will provide the audience with the experience of thinking that way.
From the Dramatia Theory Book