In fiction, major characters are central to the plot and are generally complex and three-dimensional, while minor characters are generally flat, stereotypical and not of central importance to the plot. Less time is devoted to developing minor than major characters and they tend to fade into the background of the story.
The major characters of a story are the protagonist, who is central to the main plot, and the characters around whom the various subplots revolve. The minor characters are comprised of all the other characters in the story who are of lesser importance. Minor characters generally serve a purpose as a plot device or as part of the setting, and once that purpose has been served, the reader generally does not expect to encounter them again, whereas the reader always expects to encounter major characters again until the resolution of conflict has been achieved.
These major characters are more complex and conflicted than minor characters, displaying nuanced personalities which evolve over time, rather than the mostly static and stereotypical personalities of minor characters. Minor characters are often stereotypical and two-dimensional because this ensures that they do not stand out or draw too much of the reader's attention, making them easily forgettable.