On his blog, Peter Adeney presents thrift as liberation rather than as deprivation. Photograph by Michael Friberg for The New Yorker

Mr. Money Mustache, the father of Mustachianism, isn’t perfect. He allows himself occasional luxuries, gets drunk now and then, and admits to two regrettable “five-to-ten-dollar mistakes” in 2015. The first was buying his ten-year-old son, Simon, a mini-Rubik’s Cube, which broke when they tried to take it apart. Junk. The other was putting several slices of leftover mushroom pizza in the same Tupperware container as some plain slices, which Simon, citing the mushroom taint, then refused to eat. There was a thirty-dollar mistake, back in 2010: Mr. Money Mustache built a rig for a storage box attached to the rear of his Scion hatchback, but the heat of the muffler melted a hole in the box. He modified the design, then wrote about it on his blog. The post, called “Turning a Little Car Into a Big One,” was an ode to the ingenuity of his storage box and to the underlying good sense behind owning a cheap, small, fuel-efficient automobile. He left out the bit about the muffler. The central tenet of Mustachianism is “financial freedom through badassity.” As the embodiment of badassity, and the exemplar to thousands of aspirants, Mr. Money Mustache must be as stingy with his counterexamples as he is with his expenditures. He has to be a badass.

Mr. Money Mustache is the alias of a forty-one-year-old Canadian expatriate named Peter Adeney, who made or, more to the point, saved enough money in his twenties, working as a software engineer, to retire at age thirty. We’re not talking millions. More like tens of thousands, and then hundreds of thousands, which he and his wife diligently salted away at a time of life when most people are piling on debt and living beyond their means. He calculated a way to make these early paychecks last using a strategy of sensible investment and a rigorous, idiosyncratic, but relatively agreeable frugality.

He is, by his own reckoning, a wealthy man, without want, but he and his wife, who have one child, spend an average of just twenty-four thousand dollars a year. Adeney is a kind of human optimization machine, the quintessence of that urge, which is stronger in some of us than in others, to elevate principle over appetite, and to seek out better, cheaper ways of doing things. He presents thrift as liberation rather than as deprivation. Living a certain way is his life’s work. “I’ve become irrationally dedicated to rational living,” he says.

He created his Mr. Money Mustache avatar as a way to tell the rest of us, with meticulous and triumphal precision, about his finances and his life style, and about how bad at math and life the rest of us are. We are debt slaves, consumer suckas, car clowns, complainy pants. His goals, he says, are: 1. “To make you rich so you can retire early”; 2. “To make you happy so you can properly enjoy your early retirement”; and 3. “To save the whole Human Race from destroying itself through overconsumption of its habitat.” The blog, which he started five years ago, is really an attack on consumerism and waste—a theology of conservation—disguised as a personal-finance advice column. The prospect of retirement is in some respects just a lure—the carrot, as opposed to the stick of his relentless polemical thrashing of anyone who thinks it’s O.K. to buy lattes at Starbucks or drive “a gigantic piece of shit that can barely navigate a parking lot.” He told me, “I’m really just trying to get rich people to stop destroying the planet.”

That may be so, but for adherents of Mr. Money Mustache the delight is in the details—the work-arounds and the actuarial calculations—and in the semi-comical swagger with which he dispenses them. He combines the deductive discipline of Mr. Spock, the D.I.Y. proficiency of MacGyver, and the gleeful certitude (and knack for coinage) of Ignatius J. Reilly. The consumer-waste complex is his confederacy of dunces.

For years, Adeney kept his identity under wraps. He fudged his whereabouts and biographical particulars even as he performed a striptease of his earnings and expenses. “It’s embarrassing to walk around in your monetary underwear in front of thousands of people,” he wrote a few years ago, as a preface to one of these self-audits. He didn’t really seem embarrassed at all. Still, he had the kind of mind—“enginerd,” as he puts it—that finds the who and where less interesting than the how much and to what end.

Gradually, he divulged more, as he warmed to the persona and to the admiration of the masses. Now his adherents know that he lives in Longmont, Colorado, a half hour northeast of Boulder—a Mustachian paradise. The town was founded by Chicagoans in 1871 as an agricultural utopia, and later thrived on the production of sugar beets. The heart of it is a grid of compact but stately homes with trees on small lots. In the past several years, a tech-based Boulder boom has spread to Longmont, lifting prices and reviving a once moribund downtown. I heard Boulderites refer to it as “Methmont,” but now it’s a craft-brew town, full of gut jobs and fixer-uppers, which Mr. Money Mustache often finds himself working on—for fulfillment, of course, since he doesn’t need money. He gets around town on foot or by bike. He uses his car only when he has to haul a load of more than a hundred pounds. He and his wife burn just two and half tanks of gas a year.

In the presence of such restraint, one can certainly start to feel like a dunce. I’ve got some tightwad cred. I’m a thermostat despot, with holes in my sweaters and duct-tape patches on my winter gear. I reuse paper towels and aluminum foil. But I also have a mortgage, a cable-TV subscription, a Burgundy fetish, an S.U.V. in a Manhattan parking garage, and a rented locker at the ice rink that costs about as much per year as Adeney has spent on gas during Obama’s second term. En route to Colorado, to see Adeney, I accumulated incidental Mustachian sins. Having forgotten a water bottle for the flight, I got one at the newsstand by the gate: $4.50. In Denver, with a snowstorm looming, I allowed Avis to up-sell me a four-wheel drive, plus access to the toll-road shortcut to Boulder, and some inscrutable new fuel-reimbursement option. Piloting a giant gas-guzzler along an empty turnpike, I concluded that I was a victim of the predatory math of the travel-industrial complex. Sucka.

When I confessed these and other transgressions to Adeney the next morning, he was not amused. When I blamed some of it on Manhattan, he accused me of “excusitis” and kept up a running critique over the next several days. “Paying for parking is a sign from God that you’re in an area not designed for a car,” he said. “You are fighting the design of your city.” Although he maintains a comical tone on the blog and in everyday conversation, he takes all this stuff very seriously, and at one point I realized that he was almost angry at me for my half-witting participation in the destruction of the world.

I met him at his house. He had on his Mr. Money Mustache uniform: plaid shirt over granddad button-top thermal long underwear, old jeans, day hikers. Adeney is one of those people whose aura morphs. He has mild eyes, which can make him seem gentle, and a ruddy complexion that reddens further when he gets worked up. His voice has a bellow mode, which he deploys mostly with irony—mock-bravado or command. When he dramatizes lame conventional wisdoms, he typically does it in the voice of the stupid adults and townspeople from “South Park.” He is fit, from all the walking and biking. He also lifts weights. When you play devil’s advocate—for instance, if you suggest that if everyone lived the way he does the economy would shrivel up—he can get riled, and you notice that he’s sort of ripped, in a ropy way.