
It's sometimes called The Monomyth, and was summarised by Campbell like this, in what I imagine was a high-pitched, squeaky voice:
"A hero ventures forth from the world of common day into a region of supernatural wonder: fabulous forces are there encountered and a decisive victory is won: the hero comes back from this mysterious adventure with the power to bestow boons on his fellow man."
I don't know about you, but there's little I like more than somebody bestowing their boons upon me.
Anyway. In his studies, Campbell discovered that the Hero's Journey is a narrative that occurs throughout cultures and history, that the fundamental structure of the story has been with us for thousands of years.
You see it in the story of Christ, of King Arthur, of Perseus, of Buddha, and of Beowulf. And these days it's applied to more or less every blockbuster movie - particularly in the wake of Star Wars (George Lucas borrowed heavily from Campbell).
And - hey - it's there in pretty much every video game, even if you didn't even realise, ya big dummy.

Zelda - The Wind Waker is a near perfect example of The Hero's Journey, but the stages of the journey can also be applied to the Mario series, Sonic The Hedgehog, and Telltale's The Walking Dead games.
You can even find it in the horrible Dark Souls series, if you try hard enough.
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In movies, in books, in myths - we're observers of a hero's journey. Typically, the main character in most works that lean heavily on Campbell - or the cultural myths that have been with us for millennia - is the most bland sort of everyman.
Harry Potter, Luke Skywalker, Katniss Everdeen, Captain America, Frodo Baggins, and Gordon Brittas are arguably the least interesting characters in their respective works of fiction. Yet they're the ones who we identify with, because they are the least defined.
Nintendo understand it perfectly. Ask yourself: who is Link, other than a personality-free heroic archetype? Can you imagine buying into an epic adventure where you played as Tingle?
Video game characters, or movie and book heroes like Potter and Skywalker, exist for us to project ourselves onto them, so that we can become the hero. In video games, that's even more literal than in movies, books or comics. The beautiful, moving and sublime PS3/PS4 game Journey was directly inspired by Campbell's work.
But, I wonder, does it go further than that when we play video games? Do they allow us to become the myth? Do you accept this Call to Adventure to continue reading?
Depending on which scholar of the Monomyth you read - Campbell was merely the first - there are several stages to each hero's journey, and a number of recurring archetypes.
The hero will also encounter characters that appear again and again in the monomyth - the Mentor (a supernatural guide who will bestow the hero with a magical artefact or ability; Harry Potter's wand, or Luke's lightsaber), the Trickster (hello, Yoda - did you know that you also double up as a mentor?), The Shapeshifter (a friend who turns out to be an enemy - or vice-versa; see Lando Calrissian), The Shadow (an evil threat, that often mirrors the hero - how many games feature dark versions of the hero?)...
Some of the stages of The Hero's Journey may repeat, some might be missing from a particular myth, but there are some that are integral to almost every mythological story, since storytelling began.
Roughly speaking, here they are, and how I think they might apply when we're playing games:
The Ordinary World: This is always there at the beginning of any journey; the world the hero lives in. In Star Wars it's Tatooine. In The Lord of the Rings it's The Shire. In the Zelda games, Link is always a simple boy, who lives a simple, rural, or forest existence. For Mario it's The Mushroom Kingdom.
The Call to Adventure: Here the Hero receives an invitation to venture to an unusual world. For Luke Skywalker it comes in the form of a hologram from Princess Leia, and is reiterated when Ben Kenobi says: "You must learn the ways of The Force if you are to come with me to Alderaan". For Frodo it's a visit from Gandalf. For Link it's probably when he meets some sort of poncey fairy, or something.
Refusal of the Call: This is a moment of doubt for the Hero. For Luke he complains that he can't leave his home planet, because he's too busy whining about all the work he's got to do. For Frodo, it's when he tells Gandalf that he can't take the ring, because he's got to stay in The Shire and lay a Hobbit egg.
Meeting with the Mentor: Very obviously, Luke Skywalker's mentor is Benny Kenobi. The Zelda games and other RPGs often feature Link learning to sword fight with an elder warrior - one who has already been on his own hero's journey. One who - as stated above - gives the Hero a gift, or artefact, to help on the coming quest.
Crossing the Threshold to the Special World: Typically, this is motivated by a loss. With Luke it's his aunt and uncle getting toasted. Spider-Man it's his Uncle Ben choking to death on some rice. For Mario it's the kidnapping of his girlfriend. It's the emotional devastation that pushes the hero to accept the Call to Adventure, and cross the threshold to The Special World.
Belly of the Whale: In Pinocchio, the Belly of the Whale is literally that. In Star Wars it's The Death Star. Campbell describes it like this: "The hero, instead of conquering or conciliating the power of the threshold, is swallowed into the unknown and would appear to have died."
Tests, Allies and Enemies: This is the most obvious one as far as video games goes. The tests come in the form of platforms and enemies, or shooting/jumping your way through a wall of aliens or terrorists, Goombas, zombies, or Doctor Robotnik's cyborg fauna. Along the way, the hero is learning new skills all the time. As we, the player, is also learning new skills and mastering older ones. Skills which are going to come in handy the deeper you venture into The Special World. Allies too - sometimes more obvious than others, will help you out. Mario has Toad and company to give him items he needs to assist him in his journey.
Approach to the Innermost Cave: Some myths feature more than one Innermost Cave or Special World, but this dark sanctum is at the heart of every Special World. Video games feature a succession of them. In Mario it's the boss level at the end of each literal special world he visits.
The Ordeal: For Mario, the innermost Innermost Cave is the ultimate confrontation with Bowser... where everything Mario - and the player - has learned through the course of his journey can be utilised to defeat his nemesis.
The Reward: For Luke Skywalker, his ultimate reward is becoming a hero and receiving a medal (later becoming a Jedi). In Mario, rewards come in the form of 1-ups, power-ups, invincibility stars, and getting a kiss off Peach. For Link it's accepting new abilities and items, rescuing the Princess, getting to put his hand down the front of Tingle's pants, etc.
The Resurrection: Sometimes this is metaphorical, sometimes it's literal. The hero dies, and is reborn. The hero must face death as a result of the Final Battle. In video games - I'm looking at you, Dark Souls, in particular - it can happen again and again...
The Road Back: This is the point at which the Hero must choose between personal gain and a greater cause. Where Luke Skywalker is tempted with the power offered by The Dark Side. Often in fiction it might also be represented by a chase - or fleeing an exploding super-secret spy base, magic castle, or space station... It's the climax to any blockbuster movie, or game.
Return to the Ordinary World: And the hero returns to The Mushroom Kingdom, back to his regular life - except that it's changed by his actions, restored and he or she has become complete and whole. And now the Hero can start bestowing his boons.

See, I've been thinking. When we play games, is there more to it than simply playing the hero?
Can we apply some of those stages of The Hero's Journey to ourselves, and not just the characters we control?
The Ordinary World is wherever we live. It's our mundane, day-to-day existence.
The Call to Adventure comes in the form of reviews, of ads, or trailers for a new game.
We might refuse the call, weighing up whether we can afford another £60 game, or if we've even got the time to play it. The mentor is represented those training levels where we learn the basic skills to play the game. The Ordeal, the Innermost Cave, The Road Back - they all have very obvious video game parallels.
Alright, I might be reaching a bit with some of them, but I do wonder if this is why games are so important to so many of us; they are subconsciously speaking to us on a mythical level. Every time we play a game, we are going on our own Hero's Journey. We are escaping to Joseph Campbell's Special World, and then we make our return. For a time we become a hero - and not even in a paying-it-lip-service sort of way; some deeper part of our id gets its itch scratched.
We've all grown up surrounded by these myths, which transcend religion, race, or geography - because they recur in every culture. When we embark on our own Hero's Journey within a game we're addressing something that we've all absorbed without realising. Something that has become part of us.
The desire to be a hero in our own lives, or something. I dunno, yeah. Whatevs. Latersbye.