I found this post very thought provoking and decided to use it as inspiration for my own musings on our main characters.
During my day job, I teach high school English, and one of the earliest vocabulary lessons is teaching the definitions of various literary terms, "protagonist" and "antagonist" being two of the first. Like any good teacher, I routinely steal fiercely and unapologetically from the vast array of Internet sources out there. However, too many powerpoints, slideshares, YouTube videos, etc. say the same slightly misleading thing:
"The protagonist is the main character, hero, and good guy."
"The antagonist is the villain or bad guy."
I'd like to propose the motion to forever strike these definitions from the record. All in favor, say Aye! I'm not even going to take a vote on all opposed.
Now that that's taken care of, let's redefine these terms.
This is how I teach protagonist and antagonist:
The protagonist is the character the author focuses his or her lens on most intently. The protagonist always, always, ALWAYS wants or needs something, and the wanting and needing of this particular thing is what drives the central conflict of the story. This can be something as simple at the start of a story as wanting to get to the bus stop or something as complex as wanting to be loved. The motivations of a protagonist can change throughout the story, but the moment this character stops wanting or needing something, the story is over.
The antagonist, therefore, is any person or thing that stands in the protagonist's way of getting what he or she wants or needs.
These definitions allow for the truth of characters. Not all protagonists are good. Not all antagonists are bad. In fact, there are many stories lately where the protagonist may be extremely unlikeable. In Gillian Flynn's GONE GIRL (or really any of her 3 novels), the main character is not likeable by any traditional qualifications. However, he or she still wants or needs SOMETHING, and other things are in the way of the reaching of whatever goal that is.
In one of the short stories I teach my 9th graders (Langston Hughes' "Thank You, Ma'am"), Roger is the protagonist and Mrs. Luella Bates Washington Jones is the antagonist. And yet, in many ways, Mrs. Jones is the more likeable character. She is not a villain, and in the end is, in fact, the person who gives Roger what he wants (money for blue suede shoes) and needs (kindness/love). And yet, the lens is focused on Roger. We enter his consciousness in the limited third person narration. We know what he wants and needs, and this woman who drags him up to her apartment after he tries to rob her is the only thing standing in Roger's way of him walking away with achieving his goal of getting blue suede shoes. Mrs. Jones may seem like the bigger hero, but the authors lens is not focused on her story, just on how her story affects Roger's.
In Donna Tartt's THE GOLDFINCH, Theo is arguably unlikeable. If not unlikeable, he is at least inducing of indifference as the story goes on, what with his restless lifestyle, wasteful drug use, and calculated abuse of the kindness of those he cares for most. Hobie, on the other hand, is a kind, wonderful man who gives without question to this young man who, throughout much of their friendship, abuses his grace and good nature. Hobie may not be the main antagonist of the story (in ways, The Goldfinch itself is a formidable obstacle to Theo), but he does, at times, stand in Theo's way. Theo at times is in Hobie's way (perhaps even more than the other way around).
Boris, too, is an antagonist to Theo, despite being his best friend in the story. Boris' actions constantly thwart the growth and development of Theo and ultimately lead to truly dangerous and harrowing circumstances where lives are at stake. And yet, there is something more likeable about Boris than Theo.
But in both these relationships, the author's lens is focused ON THEO, so Theo is our main character and therefore destined, in one way or another, to be the hero of his story.
So, in short, it is the wanting and needing of something that makes a character and the focus of the author's attention that makes a protagonist or antagonist. So, to return to the John Rogers quote above:
"You don’t really understand an antagonist until you understand why he’s a protagonist in his own version of the world."
Everyone is the protagonist of his own story. However, the author decides the protagonist of the story being told.