This year, the backdrop for the annual Jeffrey Fashion Cares celebration, a buoyant benefit for L.G.B.T. causes, was military might. At the Intrepid Sea, Air & Space Museum on April 4, fashion-world movers like the designers Prabal Gurung, Thom Browne and Alexis Bittar circulated under missiles, air-kissed next to gun turrets and snapped selfies with mighty aircraft.

Not that the guy stuff took center stage. Staged in a low-lit hangar where white chairs flanked a red carpet, the runway show was the pièce de résistance. With plimsolls instead of boots on the ground and only a bit of camo, it focused on the splashiest looks for the lads of summer.

Young men with determinedly blank facial expressions stalked down the runway in creations that included a slim Gucci suit whose floral print suggested Palm Beach chinoiserie; a pinstripe Givenchy pant look tweaked with images of Christ; and a long, white grandma cardigan with posies climbing up the front. (Lord & Taylor? Mais non! Saint Laurent.)

If the outfits seemed otherworldly, so, too, did the models. Bare chests (paired with seemingly everything) were impossibly sculpted. All the biceps were laser cut. Every abdomen hyper-defined. Waists tapered into nothingness, and buttocks were platonically ideal.

When the lights came up, one admirer, a towering figure with an expansive chest and farmboy good looks, confessed that the parade of fabulousness was bittersweet. “I would love to wear clothes like that,” Zach Miko said. “But they don’t exactly make them in my size.”

At 6-foot-6 and 275 pounds, the imposing Mr. Miko is hardly a mainstream customer for the designers whose looks flattered the catwalk crew (whose waists top out around 32 inches). Mr. Miko’s waist is 40 inches, and though he keeps in shape by biking, he’s free of hard edges and sharp angles. Even in the go-see ensemble that he chose for this flaunt-it evening — jeans from Levis, jacket from Hickey Freeman and the white dress shirt he wore at his wedding — he looked more like the running back who stole your heart in high school than a high-profile clotheshorse.

For all of that, Mr. Miko, 26, is the model of the moment: As the first (and so far, only) hunk signed with Brawn, a division for plus-size men that IMG started in March, he has a mandate to speak for Guys of Size longing to be au courant. And if his blue eyes and tattooed biceps look familiar, it’s because the response to Mr. Miko and his “body positive” message has been over the top. (See: “Good Morning America,” “Entertainment Tonight,” Vogue.com and British news media outlets galore.) More than 58,000 Instagram followers have bonded to the actor since he happened into modeling, making his debut online last September in the plus-size line of Target’s Mossimo collection.

Some are slavering over his body, sending nude photos, suggesting hookups and, in one case, requesting photos of his naked feet. Most of the feedback, however, has been from people sick of being fat-shamed. They tell him they’re over the moon about seeing a comrade looking sharp in clothes that they, too, can wear.

“I was always the big kid who felt like the outsider,” Mr. Miko said. “For me, the coolest thing about this is the idea that kids like me can look at a website or a magazine and see somebody their size instead of these Adonises.” He added, “I think that’s going to do amazing things for their self-esteem.”

The fashion industry has long since acknowledged plus-size women. The IMG president, Ivan Bart, said that it was the success of Curve, its division for generously proportioned femmes, that inspired Brawn. (A few smaller agencies represent plus-size models, but IMG is the first international agency to take up the cause.)

Aside from racking up diversity props for IMG (whose client list includes Gisele Bündchen and Karlie Kloss, as well as Hari Nef, who is transgender, and Jillian Mercado, who has muscular dystrophy), Curve brought larger beauties like Precious Lee and Tara Lynn to the fore and transformed the ultra-voluptuous Ashley Graham into a supermodel. This year, Ms. Graham smoldered on the covers of Maxim and the Sports Illustrated Swimsuit Issue (it featured three models, each on separate covers), as well as a special edition of Glamour.

For his part, Mr. Bart is convinced that big and tall guys are ready to break out. An Oprah-phile who lauds Ms. Winfrey’s “authenticity,” he said that his “aha moment” came in London this winter when he was scouting “more beautiful Curve women. I thought, ‘We cannot have this conversation one more minute without a male perspective.’”

A “beefy, stocky guy,” in his own words, Mr. Bart (a Brooklyn native who was a psychology major at the University at Albany) understands the kind of fashion traumas that most of his confreres don’t discuss. In a light-filled conference room at IMG’s Manhattan headquarters, he described childhood visits to the dreaded husky department and the “shaming experience” of shopping in mainstream stores, where dressing rooms are now the stuff of nightmares.

“Getting the largest size possible and then being in that room alone with the mirror: You’re like, ‘Come on, man, please, zip!’” Mr. Bart said. “You don’t fit, and the lovely store clerk will come and say, ‘Are you O.K.?’

“You’re so not O.K. You don’t even want to say, ‘Do you have another size?’ You just leave. That’s my experience.”

Offering an appropriate example of plus-size pulchritude to heavier men, as well as to the fashion industry, required a candidate who seemed relatable, in Mr. Bart’s words. The search took Mr. Bart to Instagram, where Mr. Miko, already known as Target’s big-boned dreamboat, had posted pics of himself napping with his rescue dog; mugging with his adorable wife, Laura Miko, an actress and fitness model; and gamely modeling an elf-themed sweatshirt that implored, “Take Me Gnome Tonight.” No pretension there.

Moreover, Mr. Miko wasn’t afraid to show his feelings. He had spoken up on the love-your-body site Chubstr, saying all the right things about celebrating one’s genetics (“Most men still want to be Hugh Jackman; I want to be John Goodman”) and sharing moments from the plus-size modeling scene. On his initial shoot for Target, a job he had gotten because his manager spotted a request for a larger model on Facebook, medium-size shirts had arrived at the TriBeCa studio by mistake. Humiliated, he had faced the cameras with the too-snug shirts sliced down the back.

Mr. Miko had better luck with subsequent shoots for Target and for clients like the British plus-size label Bad Rhino. And his Brawn portfolio would make it clear that he could look the part of a bon vivant or even a bombshell. “The photo with the great black T-shirt, where his own tattoos are showing, is one of the hottest, most desirable — men, women, everybody is passing out and dying,” Mr. Bart said.

In a telephone interview, Ms. Graham said: “I’m excited for what’s to come for Zach. I haven’t met him yet, but I’ve seen the amazing photos that he did and I can see why they signed him as the Brawn man.”

In the light of day, it’s hard to believe that Mr. Miko once loathed his body. Relaxing at Rockwood Music Hall, the Lower East Side club where, until recently, he worked regularly tending bar, he looks like a gorgeous lumberjack in plaid shirt, jeans and vintage boots from L.L. Bean: The jowls and jiggles celebrated by dad-bod enthusiasts are M.I.A.

Even so, Mr. Miko said that his size has defined his life, and coming to terms with it was a battle. Though his wife always told him he was “perfect,” not until he began modeling clothing that flattered his body did he begin to feel his own power. “I don’t remember when I learned that being big was a bad thing,” he said, “but as a kid that’s what I thought.”

Raised in a Roman Catholic household in Stratford, Conn., where his father was in the medical-supply business and his mother was a receptionist, Mr. Miko reached 6-1 by the time he was 12. Bullied at school, shunned at dances by girls “who were afraid I’d step on their feet,” he channeled his energy into becoming a stand-up small-town kid. His credits included altar boy, Little Leaguer, rock-band guitarist, drama-club impresario and, inevitably, Eagle Scout.

“I never used my size in an aggressive way,” he said. “I tried to be funny and charming. I wanted to be one of the guys.”

Blending into the crowd, however, was impossible. While his peers could cruise for clothes at the mall, Mr. Miko wore hand-me-downs from his 6-5 father, whose wardrobe came from big-and-tall catalogs.

With the approval of his parents (who he says were extremely supportive), Mr. Miko worked with a personal trainer and began dieting at 13. “For years, it was a struggle,” he said. At times, he dropped weight. “I look at pictures of me when I was 17, and I was thin,” Mr. Miko said. “But I always felt big. I had wild body dysmorphia.”

A creative sort who loved storytelling and science fiction, he embraced acting in high school and, later, at Albertus Magnus College in New Haven. After two years, he transferred to the American Academy of Dramatic Arts in New York, where he graduated in 2011.

Since then, Mr. Miko has snared parts in productions including the web series “Rock-Star Cafe,” a children’s theater production of “King Arthur,” an Allstate commercial and even (for a nanosecond) “The Wolf of Wall Street.”

Now waiting to hear about auditions that he did during the pilot season, Mr. Miko still performs with his comedy duo, the Dreamstalks, singing “children’s music from the point of view of jaded adults.” Glam, it is not, but, like Mr. Miko, it’s wry, bold and totally charming.

So where will America’s top plus-size male model be at this time next year? At the very least, he will be supporting other brawny dudes in distress.

Recently, Mr. Miko took up the fight against American Eagle, which had released videos of undie-clad guys, from svelte to chunky, musing about body image. Body-positive advocates applauded the company for promoting diversity until April 1, when American Eagle announced that the clips were parodies. The real message, the company said, was that it would stop retouching photos of male models in swimsuits and underwear.

Mr. Miko didn’t appreciate the joke, and he criticized the company on Instagram. “I don’t think they meant to be malicious,” he said recently. “But they were saying to all these guys, ‘Celebrate the way you look.’ And then it was, ‘Never mind, you still look funny.’” (Since then, the company has begun to explore using more models with diverse body types.)

And then there are those — some, in the fashion industry — who ask whether body positivity is a whim. Even as plus-size hunks besiege IMG and Mr. Bart scouts for more Zachs, “I tell them that this is something people want,” Mr. Miko said. “This is something people crave. I hope it’s not a flash in the pan.”

In any case, Mr. Miko, Zachlander to his friends, is holding nothing back. Last month, he shared a revealing photo with his multitude of followers, not as a sweetly confident grown-up, but as a big-boned, tentative-looking child with braces. Nothing about him suggested he would grow up to be a model, but the boy himself was beautiful.