As a boy in New Zealand, Taika Waititi went through a phase of obsessively drawing swastikas all over his notebooks. He knew what Nazis were and what the symbol represented, he says. “But you tell a kid they’re not allowed to do something, that it’s the worst thing to do, and they automatically want to do it.” The transgressive thrill was usually fleeting, he admits. “I’d instantly feel really guilty and turn it into a window.”

Ordinarily, it would be a matter of some concern if that swastika-fixated child grew up to cast himself as Adolf Hitler in his own movie. Jojo Rabbit is a comedy about a wartime German boy whose imaginary friend is, indeed, Hitler. But this is Taika Waititi: not only is he a self-identifying “Polynesian Jew” (his father is Maori; his mother’s father was Jewish), but one of the most likable people on the planet.

As with his dress sense, Waititi’s comedy compass has been unerring in recent years, both in front of and behind the camera. His previous film as a director, Thor Ragnarok, broke him into the mainstream after a decade of steadily growing appeal that became too big to describe as “cult”. Now Waititi seems to be everywhere. Along with his compatriots on Flight of the Conchords (Jemaine Clement, Bret McKenzie and Rhys Darby), for which he has writing and directing credits, Waititi has been ambassador for a brand of comedy that seems to be quintessentially New Zealand: modest, understated, deadpan even when surreal, rooted in the essential crapness of life. “Rhys Darby called it the comedy of mundanity,” says Waititi, “focusing on just the most boring parts of life and then trying to find the funniest aspects of that.”

This very local sensibility has turned out to have global appeal. Darby is to be found in the latest Jumanji movie, Clement is filming James Cameron’s Avatar sequels, and Waititi is everywhere you look: Star Wars spin-off The Mandalorian; Ryan Reynolds’ next blockbuster, Free Guy; cult animation Rick and Morty; James Gunn’s Suicide Squad; and a Time Bandits reboot. His 2014 vampire comedy What We Do in the Shadows is in its second series on TV. A new Thor sequel is also in the pipeline, but currently he is in Hawaii directing Next Goal Wins, based on the true story of the world’s worst national football team, and starring Michael Fassbender.

Waititi with Roman Griffin Davis in Jojo Rabbit. Photograph: Kimberley French/Twentieth Century Fox

“I’m going to drain myself, then I’ll fade away and be like a dried husk, blowing in the wind,” he jokes. “Some would say I’ve got too many things going on and I should just stop saying yes, but most of them are a little ways off being made so I’ve got time to figure out how to make the schedules work. But yeah, I’m busy for the next few years.”

Jojo Rabbit feels like Waititi’s riskiest proposition so far. Waititi as Hitler is the attention-grabbing headline, but the story’s real focus is the relationship between Jojo, a lonely boy too timid for the Hitler Youth, and a Jewish girl he discovers his mother is hiding in their attic. Inevitably, Jojo’s prejudices are challenged. (“Where are your horns?” Jojo asks her. “I’m too young. They grow when you’re aged 21,” she replies). The movie was adapted from a serious novel – Caging Skies by Christine Leunens – but the Hitler character was Waititi’s own addition. He was initially drawn to the story’s German point of view, he says. “I’d never really seen that before and never seen it done in my style or my sensibility.”

Portraying Hitler was never a career goal. The studio only agreed to make Jojo Rabbit if Waititi played the role himself. “It just felt uncomfortable,” he says. “The clothes were uncomfortable, the glue-on moustache was uncomfortable, and I had to have my hair dyed and straightened, which just made me feel weird all day long.”

The cast and crew felt the same, he says. “I like to be everyone’s friend as a director, to have a nice familial feel on set, and I’m trying to encourage sharing of ideas and a cool, creative space … but I’m dressed like Hitler. It just changes things, really.” It’s hard to tell whether this is Waititi being serious or another deadpan punchline. He avoided going full Hitler wherever possible, he says: “I would take off the moustache whenever I wasn’t in the scene, and I’d wear a hat, and always take off the jacket because you don’t want to be walking around with a fucking swastika on your arm trying to direct kids.”

Waititi’s buffoonish, immature Hitler is by no means a faithful impersonation and it is not supposed to be. “It’s a 10-year-old boy’s idea of what Hitler is. He can only know what a 10-year-old knows,” Waititi reminds me, adding that Jojo’s father is also, significantly, absent. But still he has a careful line to tread: this is Jojo’s supportive ally, but he is also the most evil man in history. “I didn’t want to make him actually likable or sympathetic, that would be too twisted.” I suggest that Waititi’s Hitler cannot avoid being likable, because he is being played by Waititi.

Waititi, Jonathan Brugh and Jemaine Clement in What We Do in the Shadows, 2014. Photograph: Allstar/UNISON FILMS

“But that’s OK,” he replies. “That’s not agreeing with the character. I think it’s actually better that way because, as uncomfortable as it is, you have to understand why he [Jojo] enjoys hanging out with him. And actually, if he’s horrible and evil, that makes [Jojo] evil, because he’s conjured him up.”

This contradiction runs through the whole movie. The opening sequence, for example, juxtaposes actual footage of Hitler rallies with a German-language cover version of I Want to Hold Your Hand. “Watching some documentaries on the Hitler Youth, people at his rallies were crying, some were fainting, and they were scrambling to try and reach him. It just reminded me of Beatlemania footage,” explains Waititi. “He was basically the Beatles of Germany in the 1930s.”

Such blunt comparisons could easily be taken out of context, or even used for the exact opposite purpose to what Waititi intended. But Jojo Rabbit’s broader message is obviously intended to chime with our present day. “Cut to 2016,” he continues, “when a guy was appealing to a lot of people in the US who felt like they didn’t have a voice and were left out, and at the end of a depression, and it’s a very similar situation. People will follow anyone if they’re inspiring.”

Jojo Rabbit has had a mixed reception. It won the coveted People’s Choice award at the Toronto film festival earlier this year, a harbinger of future Oscar-winners such as Green Book, 12 Years a Slave and The King’s Speech. But some critics have found Waititi’s sensibility an awkward fit with the subject matter: either too safe and sentimental to really hit home, or too stylised or sanitised to do justice to the horrors of war and indoctrination. One reviewer described it as “part [Wes Anderson’s] Moonrise Kingdom, part The Boy in the Striped Pajamas, and all shamelessly offensive”.

How does he feel about the fact that some critics have found the film offensive? “Who was it? Tell me their names,” he asks in feigned outrage. “But I think it’s pretty loved, actually. There’s not many of those people taking offence, and going into this, I always knew it would be a little bit divisive. But I didn’t want to make a film that every single person loved and thought was a charming, whimsical tale about a boy that finds a girl in his attic. That, to me, is incredibly boring and absolutely pointless.”

Waititi on the set of Jojo Rabbit. Photograph: Kimberly French/AP

He has always had a way of inserting humour into otherwise grim situations, and his comedy has never been without purpose. “Comedy has always, for thousands and thousands of years, been a way of connecting audiences and delivering more profound messages by disarming them and opening them up to receive those messages. Comedy is a way more powerful tool than just straight drama, because with drama, people tend to switch off or feel a sense of guilt, or leave feeling depressed … Often it doesn’t sit with them as much as a comedy does.”

In that respect, Jojo Rabbit is not so different from Waititi’s other movies. In 2010’s Boy, for example, Waititi played an absent father in a nowhere coastal New Zealand town whose hero-worshipping son doesn’t realise what a self-serving prat he is. Beneath the Michael Jackson jokes and quintessential New Zealand humour, Boy was a film about abuse and neglect.

Similarly, 2016’s Hunt for the Wilderpeople is a comedy about the child foster care system and people living on the margins. What We Do in the Shadows is really an allegory about the treatment of immigrants. Even the jokey Thor Ragnarok smuggled in a message about wealthy civilisations erasing their history of colonial violence and exploitation. In other hands, these themes could have made for gritty social realism. In Waititi’s, they have become delightfully offbeat, heartwarming comedies. At least when he gets the balance right. Jojo Rabbit is a test of whether Waititi’s “comedy of mundanity” can illuminate the banality of evil, or whether it can only turn a swastika into a window.

Jojo Rabbit is released in the UK on 3 January