My characterization video makes a statement that some people will think is incorrect. I say that the protagonist is “the good guy,” as opposed to the antagonist, who is “the bad guy.” This is an oversimplification of the sort that teachers often use when introducing complex concepts to young people. The kids get the gist quickly and can be taught the finer points as they try to use the terms. I go on in the video to say that not all main characters are protagonists.
And that’s where some viewers will protest.
In the past, I have thought—and taught—that protagonists and main characters were the same thing, because I’ve seen the terms used interchangeably. But I think the words protagonist and antagonist are a matched pair; they are opposites, like pro-slavery and anti-slavery.
Furthermore, I like this distinction between protagonist and main character, because it serves a useful function. No one would disagree that the murderer Raskolnikov is the main character of Crime and Punishment. The scheming Richard III is absolutely the main character of the play that bears his name. But are these characters protagonists? If you believe that protagonists and main characters are synonyms, then yes.
But if you want a distinction that says that Raskolnikov is the main character, but is strongly unsympathetic, or that Richard III is at once the villain and the main character, then the distinction between the two terms serves a purpose. They are main characters, but not protagonists. The distinction adds utility to the language.
So, my definition of these terms is what lexicographers call “prescriptive” as opposed to “descriptive.” This is what the words can and should mean, not necessarily what a lot of people think they mean. At the very least, protagonist has positive and heroic connotations while main character’s connotations are neutral.
Language is dynamic, personal, dependent on context, and reasonable people can certainly disagree about what words mean. in the case of protagonist and main character, I side in favor of greater utility because fine distinctions are what make English both nuanced and precise.