So, I recently directed Henry IV, Part One for the Hawaii Shakespeare Festival, and I noticed something curious—the title character, the main character, the protagonist and the hero are four different people. Check my math:
Title character—King Henry. Obviously.
Main character—Falstaff. He’s got by far the most lines and scenes. He’s also the most memorable (and most quotable) character in the play.
Protagonist—Hotspur. He’s the only character with an overt agenda. He drives the action of the play by launching a rebellion against the throne.
Hero—Prince Hal. Although “hero” should probably be in quotes because he’s kind of an asshole if not an outright sociopath. Shakespeare casts him in the hero role, though. Hal rescues his father, quashes the rebellion and defeats Hotspur in single combat.  And, of course, he goes on to become the much beloved King Henry V.
Now Shakespeare was probably more concerned with theatrical (and political) exigencies when he wrote Henry IV, Part One than the distinction between main character, protagonist and hero. And today we often use these terms interchangeably because they’re kinda the same thing, and everyone knows what we mean anyway.  But I think it’s worth differentiating them because it can make for more interesting stories when they don’t align.
These are my definitions:
Main character (MC)—The focal character. The one that takes up the most room, on the page or in the imagination.
Protagonist—The character who makes the story happen. The one that overcomes obstacles in pursuit of their objective.
Hero—The good guy. The character we’re rooting for. Typically the one with the greatest arc.
Let’s look at some possibilities.
MC is the protagonist and the hero.
This is the standard hero’s journey formula. The default. But don’t knock it, it still works. Henry V fits the bill as do Jaws  and, famously, Star Wars. 
MC is the protagonist but there is no hero.
There are three variations on this scheme, depending on the severity of our MC’s flaws: classic tragedy, the anti-hero and “modern literature” (which is far too sophisticated to embrace the simplistic duality of good and evil).
Macbeth falls into the first category. He’s hailed as a hero early on, but a malicious prophecy and his own “vaulting ambition” (spurred on by his wife) set him off on a murder spree.
Hamlet is more of an anti-hero; his angst doesn’t rise to the level of a tragic flaw. Hamlet wrestles with the notion of heroism without every fully embracing or rejecting it, much like the Edward Norton character in Fight Club. (It’s no coincidence that both characters have mommy issues and absent fathers.)
Finally, you’ve got those MCs who are more feckless than rebellious, and for whom heroism was never in the cards. I’d put Richard II in this category and the James Dean character from Rebel Without a Cause; they just. can’t. even.
MC is the protagonist but not the hero.
Distinct from the above in that there is a hero, but they’re not the main character. Typically the villain’s POV. Richard III, for example (Lancaster is the hero), or Dr. Horrible’s Sing-Along Blog (Captain Hammer, for all his flaws, is the hero).
MC is not the protagonist and there is no hero.
Othello. You saw that coming, right? Iago is the instigator, but Othello is the MC. And sadly for Desdemona, there are no heroes in sight.
MC is the hero but not the protagonist.
It’s been awhile since I directed King John, but I think it fits. King John is the title character and the protagonist (he sets the agenda), but the Bastard is the main character and the hero.
On the pop culture side, there’s Die Hard. Hans Gruber, one of the all-time great movie villains, is the protagonist of what could have been an epic heist film if only he’d had the foresight to be directed by Steven Soderbergh. John McClane is our main character and hero, but Gruber’s antagonist. 
MC is the hero but there is no protagonist.
A lot of older children’s literature falls into this category—stuff just happens. Consider The Lion, The Witch and the Wardrobe where the Pevensie kids are largely reactive. They’re the main characters, but they don’t really set out to do anything, and they become heroes because their mere existence satisfies a prophecy. I don’t have a Shakespeare example for you. Let me know if you can think of one.
There are a lot of permutations; I won’t run through them all. Some conjure up specific styles or stories others … don’t. Those blank spaces on the map are intriguing. Could they work for stories? Should they?
Next time: Styling the Fight
 Fun fact: historically, Hal and Hotspur never met on the field of battle. Hat tip to Kahana Ho, dramaturge, lighting designer and Peto from Henry IV, Part One.
 You can hop on Google right now and find each of these words defined in terms of the other. But that’s the internet. Do not trust it. The internet is made of lies.
 I once took a workshop with Steven E. De Souza, screenwriter of Die Hard, where he claimed that the shark was the protagonist of Jaws. Why? Because Brody, Hooper and Quint, in opposing the shark, were antagonists.
Sorry, Steven. You’re a national goddamn treasure, but that’s nonsense. The shark has no agenda. It’s just swimming around being a shark, not making plans. Maybe you were thinking of Jaws 4: The Revenge where a great white follows Brody’s family to Florida for, well, revenge. (Yes, that’s really the plot.)
 George Lucas name-checking Joseph Campbell’s Hero with a Thousand Faces changed Hollywood screenwriting forever. Chris Vogler distilled Campbell’s work into a brief but massively influential memo for studio execs (“A Practical Guide to the Hero With a Thousand Faces”), later expanded into The Writer’s Journey: Mythic Structure for Writers.
 You could make the case that McClane is the protagonist—his agenda is “trying to reconcile with his wife”—but that’s hardly the main action of the story.