Is Adventure Time the weirdest kids' TV show ever?

Welcome to the Land of Ooo, a world where rainbow-coloured unicorns bark in Korean, vibrating worms elicit hallucinogenic nightmares, and where Abraham Lincoln is still alive and reigns as the "King of Mars". Ooo is also home to Finn, a courageous, stick-limbed boy, and his best friend Jake, an elasticated, shapeshifting dog. They're the stars of Cartoon Network's Adventure Time, a cartoon which may well be the most imaginative – and indeed entertaining – on TV.

Like SpongeBob SquarePants and Yo Gabba Gabba! before it, Adventure Time has found that sweet spot between pre-teen adoration and countercultural cool; it's the latest "kids' show that it's OK for adults to like". Matt Groening and Graham Linehan regularly proclaim its greatness, while Tyler, The Creator namechecked the show in his breakout single Yonkers, right after the bit about "V Tech shit and Columbine".

All of which must be a little bewildering to the show's creator, Pendleton Ward, who "just set out to make a children's cartoon. I wanted a cartoon that felt nice, that I would have enjoyed as a kid."

Ward, 30, grew up in San Antonio, Texas and says that his animation career started in "first grade, making flickbooks on Post-it notes". His passion for cartoons led to him leaving Texas to enrol on the animation course at CalArts, LA. Things really kicked on when, after graduating, he created a proto-Adventure Time short for Nickelodeon's Random! Cartoons series, with early incarnations of Finn and Jake receiving a pep talk from Honest Abe on Mars.

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"I just lucked out," is Ward's overly modest take on how he got the gig. "I pitched my show and they liked it and picked up the pilot. It's not a very inspiring story."

Perhaps more inspiring for prospective animators is what happened next. Ward's adventure short went viral, with over a million views online, and after a short apprenticeship as a storyboard artist on Cartoon Network's The Marvellous Misadventures of Flapjack, he was given the opportunity to turn Adventure Time into a full series. Ward took the loose, sketchy animation of the short and expanded it into something noticeably bigger and brighter. The result was a fizzing, iridescent sugar rush of a show, detached from the spangly, shallow pre-teen dramas and lumbering faux-anime that seem to dominate children's TV. At its best Adventure Time feels like it can go anywhere and do anything, a spirit of curiosity best exemplified by the show's leads. Finn and Jake spend most of their time rescuing – or being rescued by – princesses and the rest exploring monster-filled caves. Ward credits this spirit of outdoorsiness with a childhood spent doing quite the opposite. "I was a small fat child who never left the house," he admits. "I wasn't a big adventurer and then I had a show that I was finally able to plug all my [indoor] adventure experience into."

Like many of his Hollywood peers, Ward's influences are largely televisual, and Adventure Time has a pop culture-infused style. The music playfully references 8-bit videogame soundtracks, as well as folk, R&B and hip-hop, while the likes of Emo Philips, Kristen Schaal and Henry Rollins – as a rainbow-coloured unicorn, no less – provide the voices. Princess Bubblegum, ruler of the Candy Kingdom and object of Finn's affections, is informed by the female characters in cartoons that Ward had crushes on as a kid. "I liked Velma over Daphne in Scooby-Doo," he laughs. "I liked the more artful fraggle in Fraggle Rock, who was really sensitive and liked poetry." Ward reckons that female characters on children's TV are made from "cliches and stereotypes", something he tries to avoid. "With girl characters they're either dumb or incredibly smart," he argues. "They're either really girly or incredibly tough. I'd just like to find a normal girl, a friend who's nice to know. And that's what we do with the girl characters."

'I was a small fat child who never left the house. I wasn't a big adventurer and then I had a show that I was finally able to plug all my [indoor] adventure experience into'

Unusually for a cartoon, where characters are often stuck in a permanent childhood, the heroes of Adventure Time age as the show develops, quietly inching towards adulthood. It's this sort of nuanced, thoughtful writing that undercuts any accusations that Adventure Time is Adult-Swim-stoner humour hawked to the under-12s, and perhaps one of the key reasons for its success with the discerning late-night crowd. Throughout there's an emotional intelligence to balance the show's oddness. But, boy, is Adventure Time odd: frogs contain portals to other dimensions, bears hold raves in a giant's stomach, and dishevelled gingerbread men issue monologues about a "cosmic dance of bursting decadence", whatever that means.

Ward is at pains to point out that this tone – which he describes as shifting between "weird" and "really grounded" – is the result of a collaborative effort, attributing the subversive style of the Land of Ooo to a team of writers and animators, in particular the graphic designer Ghostshrimp, who creates the shows' backdrops.

"We did an episode where Finn and Jake go to these different netherworlds. They found Death in his domain, and Ghostshrimp just filled it with burnt-out cop cars," he laughs.

As Adventure Time nears its half-century of episodes, the series continues to explore darker and stranger themes while remaining accessible and fun. Ward remains excited about its continued development, and is threatening further experimentation: "The show's just getting weirder and, I think, more interesting to watch."