Nicola Formichetti is sitting cross-legged on the floor of his vast Tribeca loft, which is filled with carefully arranged trinkets that he has collected over the years. There are countless stuffed pandas hauled back from Japan, stacks of books and vinyl records, and papier-mâché Day of the Dead statues strategically grouped on side tables. "I travel to Mexico often and get these every time in a little village outside of Tulum," he says. "Who doesn't love zombies? I love zombies." On this unseasonably cold day in May, the 37-year-old designer is wearing his signature tight black tank top, thick-soled creepers, and a belt with a giant bronze buckle in the shape of a winged lion, an ancient symbol of Venice, where the Tokyo-born designer launched his first collection as artistic director of Diesel in April, dressing lithe models—both male and female—nearly identically in dark-wash perforated cropped jackets, oversize army parkas, and paint-splattered faded jeans. "It's not about unisex as much as sexless," he says of the collection, gently tossing a ball to his two miniature Pomeranians, Tank and Bambi. "I think it's so sexy that girls can wear men's clothes, and sometimes I wear girls' T-shirts and it's . . . it's mixed."

A former club kid who transcended the fashion-world bubble as Lady Gaga's stylist, Formichetti caught Diesel founder Renzo Rosso's attention in 2011 while working as the creative director for the Parisian label Mugler. "I spent four hours going through the Mugler pop-up shop," says Rosso of the New York City–based retail space that was designed to look like the jagged, mirrored insides of a disco ball. "The presentation and every single item were just unbelievable." Rosso, the 58-year-old president of OTB—the holding group that controls Diesel, Viktor&Rolf, Maison Martin Margiela, and Marni—tapped Formichetti as Diesel's first-ever artistic director in April 2013. "I lost the personal touch with Diesel," Rosso admits. "It became crucial for me to have a person to rely on for everything creative."

For a designer who plucked a model named Zombie Boy (80 percent of his body is covered in tattoos) to headline a 2011 Mugler campaign, Formichetti has a fairly simple goal for the 36-year-old clothing line. He wants to focus on what the brand did best during its heyday in the late nineties: military, leather, and denim. In other words, make clothes that people actually wear. "With Gaga and Mugler, I was only doing my fantasy clothing," he says. "I don't want to just do crazy stuff anymore. I actually saw someone wearing one of my T-shirts yesterday, and it's just a really nice feeling."

A classically trained pianist from the age of 10, Formichetti grew up in Japan and Italy and moved to London to study architecture but "ended up going clubbing instead!" he says with a laugh. "All I knew about London is that Camden is where all the punks hung out, and I had to be in Camden. It was fun until the money from my parents stopped coming." In the late nineties, he launched The Pineal Eye, a toy store–cum–fashion space, with friend and retailer Yuko Yabiku, in London's Soho neighborhood. The popularity of the shop led to a commission by the stylist Katy England for a monthly first-person page called "Eye Spy" in Dazed & Confused. By 2008, Formichetti had worked his way up to creative director of the magazine. He met Lady Gaga on a cover shoot for V magazine, going on to style her most iconic outfits (including that meat dress). "I signed on with no idea what would happen, and it was immediate," Formichetti says. "She was the one who taught me about Twitter—the way you work with it, you know? I do think we created history."

His unlikely career trajectory has made him something of a cool kid among cool kids, long revered by the fashion illuminati for his innate talent for uncovering what's next. Consider, for example, his first two ad campaigns for Diesel. An acolyte of Twitter and Instagram (he currently has 254,000 followers on the former), Formichetti took to the Web, casting real people he found on Tumblr—a graffiti artist, a wheelchair-bound blogger—as models, snapping both media outlets and a jaded Internet generation to attention. "If there's one significant change since Nicola took over, it's his uncanny ability to revamp the brand's image and marketing strategy," says street-style photographer Tommy Ton. "He has a certain way of capturing the Zeitgeist, selecting and embracing the right faces."

One of those faces is the 25-year-old rapper Brooke Candy, with whom, along with photographer Steven Klein, he collaborated on the macabre, over-the-top video for her bravado-riddled single "Opulence." "With Brooke, he's pulling in the super-glam, the grills, the film noir reference to Sam Fuller's The Naked Kiss," says Guy Trebay of the New York Times. "It's always surprising to me how limited the fashion world is in general, the constant recycling of the same five references. And here's somebody who's going to throw in the kitchen sink but still sell garments at the end of the day."

Formichetti has never been precious about using other people's work in his own. "That's what I always say to young creators," he says. "Just copy, look around, mimic things, be free." Still, it's not as if he's simply telegraphing back to us a shirt or a pair of shoes only slightly tweaked from their original iteration. You get the sense he sees all art and fashion, even the sacred cows, as fair game, transforming and manipulating something until it's unmistakably his own. Even his Birkin bag, hanging from a bookshelf in his living room, marked up in black-and-white doodles, is hardly recognizable. (He says he bought it en route to Bali and began drawing on it at the beach, simply veering off the pad of paper he had with him.) "I never went to school, but I feel like I studied a lot through working," he says. "It's probably a good thing. In the beginning, if I knew how difficult [this industry] was, I don't know if I'd be able to do it. I guess I was kind of fearless."

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