Cartoon Network

Nobody really expected a cartoon featuring post-apocalyptic candy kingdoms and Korean-speaking unicorns to become a children’s-television success story. Nor did anybody expect that same show to be a success story with just about every other demographic out there, either.

But that’s exactly what happened to Adventure Time, an animated series following the exploits of Finn, a 14-year-old boy, and his best friend, Jake, a walking, talking and shape-shifting dog. Together, the pair has inspired a loyal legion of fans of that number in the millions. And, now in its fifth season, the show that began as a one-off animated web short is coming back to the medium on which it originally debuted: streaming video. Season one of Adventure Time will go live on Netflix Instant on March 30, with new episodes airing on Cartoon Network through December 2013. If you binged on House of Cards earlier this year, prepare your queue for a dose of trippy whimsy.

Adventure Time’s evolution from web short to international franchise has surprised and stumped even those intimately involved with the show, like John DiMaggio, the voice behind Jake (as well as Futurama’s Bender). He remembers one conversation with voice actor Tom Kenny — Adventure Time’s Ice King villain — about the show’s unexpected popularity.

“I was like, ‘I just don’t get it man,’” DiMaggio recalls. “And he said, ‘You know what? This is this generation’s Yellow Submarine. It’s that kind of world.’ It finally struck me — and I get it ever since.”

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At first glance, Adventure Time creator Pendleton Ward doesn’t seem to have much in common with his youthful protagonist. Finn is an ebullient teenager with a signature white bear hat, prone to such unlikely exclamations as “Mathematical!” and “Algebraic!” Ward, on the other hand, is a low-key 30-year-old animator with an epic beard you can “like” on Facebook. But he had the makings of Finn swirling around in his brain from a young age. A childhood interest in animation led his mother to take him to Simpsons creator Matt Groening to ask for advice – a fact Groening revealed when he crashed the Adventure Time Comic-Con panel in 2011. Later, in middle school, Ward answered a more noble calling when he rallied classmates to protect the rainforests.

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“I would do petitions and get people to give up money,” Ward says. “I thought I was a big hero when I was little. I wanted to be.”

He didn’t actually get to play the hero (albeit a cartoon version) until years later. Adventure Time’s animated short pilot was originally commissioned by Nickelodeon’s cartoon incubator program, Random! Cartoons, but the seven-minute episode leaked to the Internet and started generating viral traffic well before it actually aired in 2008. The network ultimately passed on turning Adventure Time into a regular series, but the pitch eventually found its way into the hands of Cartoon Network executives, where then-new chief content officer Rob Sorcher says its unfiltered imagination didn’t inspire much confidence.

“I was, luckily, in the position where I could afford to take a risk, because that’s what this show really represented at the time,” says Sorcher, who ultimately green-lit the show. “It was unlike any cartoon I had seen before.”

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The pilot found Finn — then-named Pen — indulging in behavior that was both heroic, like saving a princess, and totally weird — traveling through time and space to encounter Abraham Lincoln on planet Mars. The pitch stuck out for good reason, but Sorcher says it also raised a number of concerns. Its combination of fantasy, absurdity, and hints of darker humor had the potential to pull in an older crowd of cartoon enthusiasts and hipsters — less certain was if this mix would appeal to kids. And though Ward did work for the network on another show, The Marvelous Misadventures of Flapjack, it was unclear whether he could transform his pitch into a full-fledged series without losing any of its original charm.

What eventually tipped the scale in Adventure Time’s favor was the development of the show’s primary setting, the Land of Ooo. A post-apocalyptic world of magical monarchs and oddball inhabitants, Ooo finds the balance between child-friendly fantasy and more adult laughs. It’s home to vampires who drink the color red instead of actual blood, but it was devastated by war. It’s bright, bouncy and shiny, but it retains the classic feel of hand-drawn animation. It’s mostly devoid of gross-out humor, but a well-timed fart joke does not go unappreciated. The lore of Ooo is imperfect, and its mythology flies by the seats of the writing-room’s pants, but it provide a geography that feels both timeless and full of endless possibilities.

“It’s two contradictory things at once, and they somehow meld together and make a really harmonious, wonderful television show,” DiMaggio says.

Make that a successful one, too. Adventure Time draws in two-to-three million viewers each week, and the audience runs the gamut from little kids to college co-eds; 30-something guys to teenagers in the Middle East watching through scrambled Internet. The fanbase itself has become a phenomenon of its own, dressing up as (and gender-bending) the characters while churning out fan art like factory workers. Keeping the show fresh for them is no easy task, and Ward says fending off fifth-season blues is the writing room’s biggest obstacle. “The challenge now is keeping it real without jumping the shark, keeping it interesting without alienating the people who love it and watch it all the time,” he says.

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Making that balancing act more precarious is the show’s rapid evolution from an animated short to a global cross-platform franchise. After three years on the air, Adventure Time is no longer just a television program. It’s spawned a comic-book series, a graphic novel spin-off, an action figure line, an iPhone app and several video games. It has become, as Ward puts it, “an unwieldy beast.” When it comes to consistency, Ward isn’t in charge of creating every nugget of Adventure Time content, but he does work on each episode, writing outlines and developing story concepts if not writing the episode himself.

He also gets by with a little help from his friends. When Cartoon Network picked up the show, Ward brought a lot of his own people on board, including former school classmates, like Adam Muto, one of the show’s supervising producers, as well as pals from the indie-comics world. Adventure Time might seem like it’s from another planet, but whether the staff is inspired by what they did last weekend or the Dungeons & Dragons games of their youth, the show is, ultimately, the final product of a group of friends trying to write characters that feel real in a world of total fantasy.

“We try to share our inner most secrets about ourselves,” Ward says. “That’s what people can relate to, and that’s what makes the show worth watching and making for us. If it was just goofy cartoon nonsense, we’d all be bored.”

Both Ward and fans say this sincerity is the heart of Adventure Time. Though Finn’s and Jake’s adventures continue to be the main premise, the appeal of the show extends beyond that of a boy and his best friend. Over the course of five seasons, the Land of Ooo and its extended family of characters have been fine-tuned by a staff that turns even the most archetypal cartoons into multidimensional characters, injected with a little bit of humanity. Princess Bubblegum may be hot pink and girly, but don’t write her off as a ditzy damsel in distress. The Ice King often kidnaps her and others in his quest for a wife, but his back-story evokes empathy. And as Lumpy Space Princess deals with self-confidence and clashes with her parents like a typical tween, she’s still one of the most unconventional female cartoon characters on television — just listen to her voice.

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“There’s not a cynical bone in the body of Adventure Time,” Sorcher says. “That comes from Pen Ward, and that comes from the people who work on the show. That is one of the main qualities that makes this the cartoon for the next generation. They’re making it for themselves. These are the first millennial-aged animators making cartoons for the this generation of kids.”

Ward is already inspiring that next generation, too. He hears all the time from fans who send him eager emails and line up to shake his hand at panels about the path to joining Adventure Time and the world of professional animation. His advice hasn’t really changed: Don’t wait to start creating, put yourself into your work and, most importantly, do your own thing. After all, it’s what he’s been doing this whole time.

EXCLUSIVE: Here’s a scene from the first-ever CG episode of Adventure Time, which finds Ice King creating a computer virus to delete everybody except him and Princess Bubblegum. The episode premieres April 1 at 7:30 p.m. ET/PT on Cartoon Network.