It’s a warm March night in New York City. The Wix Lounge, a cooperative work and event space just off Union Square, is packed with a motley crew of corporate MBAs, entrepreneurs, and dreamers. Tonight, Wix is hosting the first U.S. installment of a popular speaker series put on by a London-based group called Escape the City. Its mission is to guide restless professionals toward alternative career paths, and everyone in the room wants to know what the man with the microphone knows: “How to Build a $70 Million Company in Two Years.”

Will Dean, the 31-year-old creator of the Tough Mudder obstacle-course series, stands before a projector screen beside his business partner, fellow Englishman Guy Livingstone, also 31. Dean is dressed in jeans and a black fleece jacket emblazoned with his company’s logo, a man running through a wall of flames. Handsome, with a boyish, aw-shucks smile, he doesn’t look like a ruthless capitalist or any of the much nastier names some of his competitors in the burgeoning $250 million obstacle-race industry use to describe him. “We’re trying to build a household name,” he tells the crowd, sounding modest and unassuming even as he describes his goals for global domination. “When a guy goes into a bar and thinks, when he tells a girl that he’s doing a Tough Mudder, that the girl knows what he’s talking about—that, for us, will be the sign that we’ve arrived.” He pauses for a beat, then delivers his punch line. “Whether the girl is impressed or not is frankly irrelevant.”

For the uninitiated, a Tough Mudder is a 10-to-12-mile run that features a set of sadistic obstacles: ice baths, fire, live electrical wires, tunnel crawls, barbed wire. Sadistic yet enormously popular. This year, Tough Mudder has registered more than 500,000 participants for 35 events, bringing in $70 million in revenue. Not bad for a two-year-old startup launched in the teeth of the recession.

“The truth is,” Dean says, his company’s growth charts projected on the big screen behind him, “this is a hundred times bigger than we ever thought.”

Raised outside Sheffield by lawyer parents, Dean attended the University of Bristol, where he graduated at the top of his class in 2003. He spent the next four and half years in the Middle East and South Asia, working desk jobs in the counterterrorism department of the British government’s Foreign and Commonwealth Office before, as his company bio says, “getting it into his head that an American MBA would be a good thing to do.” He enrolled at the Harvard Business School in 2007, and it was there that he hatched his big idea.

“I was getting into triathlon and marathon at the time,” he says at Wix. “There was something a little boring about the training component of it. It was missing the camaraderie that I was looking for. I thought, I need to create something that makes running fun.”

In the spring of 2009, Dean entered his concept for a national mud-run series into Harvard’s business-plan competition. Every professor told him it was a bad idea. Still, the proposal was a semifinalist, and a few months after graduating Dean convinced Livingstone, his mate from boarding school, to ditch a corporate lawyer job and be his COO. In February 2010, they launched the Tough Mudder website and bought about $8,000 worth of Facebook ads promoting their first event, held a few months later at a small ski area near Allentown, Pennsylvania. Then: boom!

In the past few years, obstacle racing has experienced a rate of growth that may be unprecedented in the history of participatory sports. Roughly 41,000 people entered about 20 U.S. events in 2010. This year, some 1.5 million people will enter 150 events. There are dozens of races now in the game, but the great majority of participants will sign up for one of the sport’s Big Three: Tough Mudder; Warrior Dash, a 5K race launched in 2009; and the Spartan Race series, which debuted just two weeks after the first Tough Mudder.

Each of these upstarts has already experienced incredible return on investment. Warrior Dash, which has staged 49 events this year, stands to rake in $50 million in 2012. Spartan Series, consisting of 28 events of various lengths, will bring in $30 million. But at $70 million, Tough Mudder is the lead dog. There are a number of reasons for this, including the company’s knack for crafting particularly dramatic obstacles, the company’s marketing savvy and salesmanship, and Dean’s gift for harnessing the power of social media. “We’ve tapped into humblebragging,” he says during his Wix presentation, using the Twitter-age term for thinly veiled boasting. “What we have found is that experiences, particularly shared ones, are the new luxury good.”

Some of his adversaries have a different take on why he’s been so successful. To them, Will Dean is another Mark Zuckerberg, an unscrupulous Harvard brat who took someone else’s idea and is willing to do whatever it takes to win.

IF YOU’RE TRYING TO grasp how the seemingly fringe, masochistic pursuit of obstacle racing took over the world of endurance sports, it’s probably best to focus on the same place Dean did, a 150-acre horse farm near Wolverhampton, England—home to an eccentric former British Army soldier and event promoter named Billy Wilson. Wilson, who’s in his mid-seventies, sports a bushy handlebar mustache, dresses in 19th-century military uniforms, and goes by Mr. Mouse (“I wanted a moniker representing the most humble creature,” he explains). In 1981, he teamed up with his son to run the inaugural London Marathon in a horse costume; his son was the front part, Wilson the ass. Five years later, he began staging an annual cross-country race on his farm, featuring simple obstacles like ditches and mud pits. Participants loved it. After a few years, Wilson began adding challenges that drew upon his military background: the high wall, mud bogs, tunnels.

Word spread about the brutal contest, and the event gradually grew to what it is today: Tough Guy, a 15-kilometer midwinter mud run that employs two dozen grueling obstacles and is billed as the Safest Most Dangerous Event in the World. That’s somewhat misleading. Over the years, hundreds of Tough Guy participants have suffered broken bones, over a thousand have been treated for hypothermia, and one has died. But paying customers keep coming back. By 2008, Tough Guy and its summer edition, Nettle Warrior, were attracting a combined 5,000 racers and bringing in half a million dollars in revenue. If you were a young entrepreneur looking for an event concept that might take off in the U.S., this was it.

During his second year at Harvard, Dean began researching Tough Guy and, to a lesser degree, the Strongman Run, which had launched in Germany in 2007. He showed up on Wilson’s farm in July 2008 to observe a Nettle Warrior, packing a camera and ready to take notes. He snapped photos, interviewed athletes, and jotted down his observations about demographics, obstacles, and logistics. He was impressed with the alternative vibe and camaraderie, but he was also struck by the lack of corporate sponsorships and the missed merchandising opportunities. Racers couldn’t buy mugs, bumper stickers, or photos of themselves on the course. He reached out to Wilson over email to propose doing an Independent Student Research report for his Harvard studies focusing on “the feasibility and logistics of expanding Tough Guy internationally.” The two men couldn’t have been more different, but Wilson was taken with the Harvard kid’s passion for Tough Guy and agreed to cooperate.

Dean began requesting information: company financials, accounting, access to customer databases. He wanted details on the costs of setting up a course and how Tough Guy was marketed to its target demographic. He said his project would examine “the likelihood of others copying the format”—and how to stop them if they did. “At the end of all this,” Dean wrote in an email, “I hope to be able to put together a detailed report that outlines the size of the opportunity in the U.S., a blueprint of how you might launch.”

Dean visited Wilson at his farm in early October, but by then the elder Briton had grown suspicious. He presented Dean with a nondisclosure agreement that recognized “the commercial importance” of the operations and financial accounts of Tough Guy and stated that “this information may not be used to any commercial end whatsoever.” Dean signed it.

In December, when Dean completed his report, he submitted one version to Harvard and a slightly modified one to Wilson. Both described the potential for more events, but the version he sent to Wilson omitted key recommendations for how he might immediately expand. Rather, he suggested Wilson adopt a wait-and-see approach. Wilson was unimpressed with the report, and the two men fell out of touch.

During the spring 2009 semester, Dean developed his business plan for Harvard’s competition. In it, he described an event-planning and promotion company that would host extreme endurance contests across the U.S. The plan was a semifinalist, and in May Dean graduated with honors.

“THERE’S NOT A PERSON on this planet I despise more than Will Dean,” says Joe DeSena. “Every day I wake up just out of spite for the guy.”

DeSena, 43, is a former Wall Street trader and no-nonsense Queens native who once completed two ultramarathons and an Ironman in the same week. In 2004, he created an insanely punishing annual event called the Death Race, which lasts about 48 hours and features nightmarish challenges like excavating a tree stump and carrying it to the finish or deadlifting 30-pound rocks for hours on end. Every summer a couple of hundred psychotic endurance athletes head to Pittsfield, Vermont, to try it. In the spring of 2010, believing there was an opportunity for a larger business, DeSena created the Spartan Race series.

That August, during the second Spartan Race, in Boston, DeSena noticed a plane flying over his course trailing a banner: THINK THIS IS TOUGH? TRY TOUGH MUDDER.

It was an ad for Dean’s new company, which had held its first event that May. For DeSena, the banner was a sure sign that he was entering into full-scale business warfare.

Two months later, in October 2010, Tough Mudder started going after new fans of Spartan’s Facebook page. For several weeks, anytime a Facebook user clicked the Like button on the Spartan page, they’d get an instant message: We see you like Spartan Race. We know Spartan Race is fun, but let’s be real—it’s not that tough. If you’re looking for something to really test your grit, check out Tough Mudder. Users were then offered a $10 discount on a Tough Mudder event if they entered the code “Spartan.” (Tough Mudder says it hired a third-party firm to lead this effort and doesn’t have records related to the campaign.) The messages stopped only after Facebook threatened to shut down Tough Mudder’s page.

“Imagine the balls on that kid!” says DeSena, who believes someone wrote a program to auto-send all the messages. “But I’m not going to lie to you: we would have loved to have developed the program ourselves.”

Besides battling DeSena, Dean was also taking aim at Joe Reynolds, the 31-year-old founder of Red Frog Events, who launched the Warrior Dash in July 2009. Inspired by NBC’s The Amazing Race, Reynolds sold his house-painting business in 2007 and invested $5,000 in an “active entertainment” company that would organize citywide scavenger hunts and music festivals. The Warrior Dash will see some 750,000 racers this year, making it the most popular of the Big Three. At just five kilometers, it’s a sprint compared with the 12-mile Tough Mudder, a distinction Dean has sought to exploit. Since 2011, at the three-mile mark of any Tough Mudder event participants have encountered a large sign that reads, WARRIOR DASH FINISH: BUT THIS IS TOUGH MUDDER AND YOU’VE ONLY JUST BEGUN. Translation: Warrior Dash is for wimps. (Reynolds laughs off the slight. “I view it as great free advertising for Warrior Dash,” he told me.)

Considering the money being made in obstacle racing, it’s easy to understand why Dean has chosen to be so aggressive. The sport has tapped into a latent desire for suffering and bedlam that’s as surprising as it is universal. Participants range from college students and CrossFit junkies to lawyers and military personnel. Some 50 percent of Warrior Dash racers are women. The diversity has everything to do with the way the events are positioned: they’re not just tests of your athletic fitness, like marathons or triathlons, but of your character and determination. The Big Three have also succeeded in setting themselves apart from the already-crowded endurance-racing category. By adding costume contests, live music, and staples like free beer at the finish, they feel more like counter-cultural happenings than athletic events. Tough Mudder has barbers giving free mohawks, as well as tattoo stations. So far, more than 1,000 competitors have been inked with the company logo.

For all this, participants are happy to cough up steep entrance fees. Early registration runs $60 for Warrior Dash and $100-plus for Tough Mudder and the 13.2-mile Spartan Beast. (Prices spike to $200 or more if you wait to sign up for the latter two.)

The young, fit, loyal communities these races have built are, of course, a marketer’s dream, and the full spectrum of corporate America has lined up for big-dollar sponsorships. Last December, Tough Mudder signed a two-year deal with the athletic-apparel brand Under Armour for a reported $2 million to $3 million. Dean has also partnered with Dos Equis, Degree deodorant, and Clif Bar. Warrior Dash has inked deals with Miller Lite, Reebok, and Monster Energy drink. DeSena has landed contracts with Dial soap and the Navy Federal Credit Union; in August, he announced an investment from Boston venture-capital fund Raptor Consumer Partners reported to be close to $10 million.

The primary catalyst for the industry’s growth has been social media, a tool that obstacle racing seems uniquely qualified to harness. Few things attract as many likes from Facebook friends as a photo of you looking like a Navy SEAL, hurdling over burning bales of hay. “Social media has allowed an idea like this to be adopted at a speed and scale we’ve never seen before,” says Michael Mendenhall, who is credited with building the X Games franchise when he was head of marketing at Walt Disney. “It used to take a decade or longer for something like this to take hold. Now you can do it in less than two years.”

At this Dean proved himself extremely adept from the outset. His initial Facebook ads sparked a viral campaign that attracted a whopping 4,500 runners to his first event. The Tough Mudder Facebook page has since pumped out an endless stream of engaging content, from videos and caption contests to images of participants at their desk jobs wearing the signature Tough Mudder orange headbands that are handed out at the finish line. Tough Mudder also posts updates about funds raised by entrants for the Wounded Warrior Project, a program that aids military veterans ($3.5 million and counting). By early fall of this year, Tough Mudder had 2.3 million likes, nearly as many as Spartan Race (1.7 million) and Warrior Dash (900,000) combined.

TOUGH MUDDER’S RAPID ASCENT is even more remarkable when you consider that Dean spent his first year fighting a bitter war on a second front. When Billy Wilson found out about Tough Mudder shortly after its website went live, in February 2010, he was furious. The site, which cost only $1,800 to launch, was decorated with photos and videos taken almost exclusively at Wilson’s Tough Guy.

Wilson asked Doug Brodie, his London-based financial advisor, to call Dean to try to convince him to cancel the first Tough Mudder. Dean told Brodie there was no chance; he’d already run everything by his lawyer. “You don’t need a lawyer,” Brodie recalls saying. “You need to pour yourself a big glass of wine and ring your Harvard professor, because this is about integrity and business ethics.” It was no use.

Days later, Wilson emailed Dean a death threat inspired by The Godfather: “I love horses too much to cut their heads off to impress conmen in their bedclothes. I much prefer to chainsaw down the centre of the bed and spill human blood.” He followed that with a blog post on Tough Guy’s website titled “Killing Private Mudder,” in which he stated his intent to “expose [Dean] as a scoundrel before innocent people are conned.” Still fuming, later in the month he sent out a blast to the entire Tough Guy email list that led with the question “Harvard Business School for Crooks?” In it he called Dean a “squelchy plagiarist” who “limped like a barnacle to our shit bucket” and suggested that Dean’s lack of experience might result in obstacles that could “injure and endanger” participants and “muddy the great name of Tough Guy.”

Undaunted, Dean went ahead with the first Tough Mudder as planned, with several obstacles that were almost identical to those he’d seen at Tough Guy, including underwater tunnels, wall climbs, and plank walks. A prominent on-course sign was also notably similar. Tough Guy displayed one that read, REMEMBER YOU SIGNED A DEATH WARRANT. Tough Mudder’s read, REMEMBER YOU SIGNED A DEATH WAIVER. In the hype surrounding the event, nobody mentioned the connection. The New York Times reported that “Tough Mudder appears to have found an opening in the burgeoning action-sports realm.”

Wilson’s rage boiled over. In June 2010, he filed a multimillion-dollar civil suit against Tough Mudder in a U.S. district court in New York claiming breach of contract, misrepresentation, and violation of trade secrets, among numerous other complaints. The case was eventually settled, and an agreement between the parties forbids them from discussing it, but documents obtained by Outside detail an ugly fight that began with an internal Harvard investigation.

According to university records subpoenaed by the court, administrators contacted Dean 11 days after the first Tough Mudder to inform him that they were convening a Conduct Review Board to investigate complaints Wilson and Brodie had made to Harvard.

In a response to the board, Dean wrote that Mr. Mouse was “vengeful” and “bullying” and that their relationship broke down in part because Dean encountered facts suggesting that Wilson was inflating the cost of obstacle construction, to evade taxes, and embezzling charity funds. (In January 2011, the U.K.’s Charity Commission launched an investigation of Tough Guy, which was suspended in August without having made any official determination.) Dean also claimed that Tough Guy’s accountant was “cagey” and the information he provided useless. Ultimately, Dean stated to the review board that he was proud of how he handled himself toward Wilson, who was an “irrational and unpredictable” man.

In mid-July, the review board issued its ruling, concluding that “there was insufficient evidence that [Dean] inappropriately used confidential information … provided by Tough Guy Limited in developing his own enterprise.” But the board also said that Dean had violated Harvard standards of “ ‘honesty’ and ‘integrity’ and ‘accountability’ in several important respects.” Furthermore, they wrote, “If other HBS students engaged in field work followed his example in regard to confidentiality agreements, the negative impact on the School’s reputation and its ability to secure field-based research opportunities could be significant.” The board placed Dean on alumni probation for five years.

Dean’s legal defense included claims about Wilson and Tough Guy that were similar to those he’d shared with Harvard. He again cited Wilson’s crooked accounting. Yes, the customer list had proved useful, but such lists aren’t legally considered confidential, he argued. As for the Tough Guy images he used to promote his first event, all were carefully marked “for illustrative purposes only.” He also claimed that he couldn’t have stolen any intellectual property because Tough Guy was just one of a number of existing obstacle races—there were no unique ideas to steal. (The Camp Pendleton Mud Run, often cited as the original U.S. obstacle race, was first held 18 years ago on the Marine Corps’s Southern California base.)

As the case dragged on, the brawl became public, with Tough Guy fans—and Wilson himself, some suggest—storming the comments sections of just about every Tough Mudder–related piece of media. The attacks appeared under numerous aliases, but they all shared the same charge: a Harvard guy stole the idea to create Tough Mudder, he used photos and videos of Tough Guy to promote his first event, and now he’s being sued and will probably be shut down.

By January 2011, Dean had had enough. He filed a countersuit for defamation of character. Seven months later, the parties reached a confidential settlement for both cases. According to court documents, Tough Mudder paid $725,000 to Tough Guy. But by then it hardly mattered. Tough Mudder was on its way to becoming the biggest name in the business.

DEAN PUT THE FEUD with Tough Guy behind him, but he’s still battling Spartan and others in the obstacle-race industry. In February 2011, DeSena held a successful Spartan Race at Vail Lake Ski Resort in Temecula, California, and signed a contract for another in 2012. But just before he announced the new race, Tough Mudder added a Vail Lake event to its own calendar, scheduled for just three weeks later.

Shocked, DeSena called Dean. “Will said, ‘Hand on my heart, I had no idea you were planning an event around that time,’” DeSena recalls. “I knew he was lying, but whatever. I said, ‘Let’s work this out. I’ll move my date up a month, and you move yours back a month or two so that they’re spaced out.’”

Next, DeSena heard from David Godes, one of Dean’s former Harvard professors and an adviser to Tough Mudder. “I get this email saying that if we try moving the date, it could look like collusion,” DeSena told me. “What are they teaching at Harvard? Theft Marketing 101?”

DeSena hasn’t exactly responded with passive resistance. He’s taken to flying his own banners over Tough Mudder courses (some purposefully misspelling Mudder as “Mutter”). He also dispatches street teams to blanket towns hosting Tough Mudder events with Spartan Race lawn signs, leaflets, and posters. He created a sly Facebook ad that read “Like Tough Mudder?” and clicked through to the Spartan page. In October 2011, when Tough Mudder was forced to cancel a race in central Texas due to a hurricane, DeSena offered participants free entry to a forthcoming Spartan Race in nearby Glen Rose.

At times the rivalry has played out more like a scrap between frat boys than Coke versus Pepsi. Tough Mudder responded to the Texas invite by mailing DeSena a copy of Dale Carnegie’s How to Win Friends and Influence People with a handwritten inscription and Dean’s signature: “How nice of you to offer participants free entry…. No doubt a worthy strategy to focus on those customers who have not yet done the Mudder, for the likelihood of success with those who have would seem dim indeed.” That December, Tough Mudder held its first World’s Toughest Mudder, a year-end contest that had elite Tough Mudder participants duking it out in a 24-hour challenge. According to Tough Mudder, Spartan employees were on hand measuring obstacles and rushing the finish line to hand out Spartan Race towels. Looking into this, I learned that an entrant named Todd Sedlack had tried to give his Spartan towel to the race’s overall winner, Junyong Pak. Sedlack, an EMT who’d entered Spartan races in the past, is friends with Pak and told me he thought Pak was showing signs of hypothermia. He said a “guy with a British accent” ripped the towel from his hand and screamed, “You’re not hijacking this moment!”

Meanwhile, Tough Mudder has begun tussling with some of the newer brands hoping to elbow into the obstacle-course arena. This past March, four days before an outfit called Savage Race was to hold its second event, in Clermont, Florida, Tough Mudder filed for an emergency restraining order in federal court to shut it down, claiming Savage Race was trying to confuse the public into thinking it was affiliated with Tough Mudder.

Judge Gregory Presnell refused to enact the order. “It seems unlikely [Tough Mudder] just discovered its competitor’s website and Facebook page in the past few days so as to justify showing up in court on the eve of an event, demanding a shutdown,” he wrote. In fact, Dean had met the Savage Race founders, Sam Abbitt and Lloyd Parker, at a trade conference last fall in Las Vegas, where they’d discussed their plans. “Will told me that Savage Race was not a threat to his business,” Abbitt stated in his affidavit. “He said there’s space for everyone in this industry and wished us luck.”

The Savage Race went forward, but Tough Mudder continued to press its case, using arguments that sound eerily similar to those made by Wilson and Tough Guy. A preliminary injunction, filed in late May, claimed that Tough Mudder obstacles contain proprietary designs. Once again the judge wasn’t having it. “Monkey bars, mud puddles and barbed wire are staples of obstacle courses,” he wrote. “The fact that both events include them is not indicative of copying.” In August, the two parties reached a confidential settlement.

Still, DeSena is worried about Tough Mudder’s legal strategy. “If they can get away with trade dress, they can potentially just own obstacles,” he says. “They can slowly squeeze us all out.”

FOR SOMEONE WHO HAS inspired so much anger, Will Dean sure comes across as a likeable guy. Two days after he gave his talk at Wix in March, I reached him on his cell phone at the Los Angeles Airport. He was laid over en route from New York City to Melbourne, where 25,000 Aussies would soon participate in Tough Mudder’s first international event. During the hour-long discussion, he gamely answered my questions, repeatedly insisting that he wasn’t competing with other obstacle races at all. “There’s plenty of space in this market for everyone,” he said, echoing what he’d said to Savage Race’s Abbitt.

As Dean sees it, Spartan Race and Warrior Dash offer totally different products. “We’re not a race—we ban the word,” he said. Plus, the other courses are so much shorter, they hardly compare. “It’s pretty clear we’re different concepts,” he said. “I’m sure a marathon organizer doesn’t look at a 10K and say, ‘These guys are competing head-to-head with me.’”

And while he suggested that there was probably a huge overlap in fan base among Big Three events, he told me he thinks this is good for everyone. “If anything, them being in the market benefits us, like how the Boston Marathon benefits from the New York Marathon,” he said. A number of times, he wished his competitors “good luck.”

As for upstarts like the Savage Race, he told me he viewed them in the same collegial light. The Savage Race lawsuit “isn’t us trying to be the Microsoft of the space and crush everyone around us,” he assured me, it’s about safeguarding the industry. “We spend a fortune designing obstacles and getting engineers to sign off that they’ve all been stress-tested,” he said. “If someone says, ‘Hey, our obstacles are the same as Tough Mudder’s,’ but they haven’t spent hundreds of thousands of dollars building them to specification—if they’re copying it off a photograph rather than a blueprint and the thing collapses, it’s going to make life a lot harder for everyone.” (Savage Race’s Abbitt bristled when I conveyed Dean’s concern: “Unsafe? I have a master’s in building construction. I’m licensed to build a skyscraper in the state of Florida.”)

Disasters aside, Dean doesn’t think it’s fair for other events to poach his R&D. “We’re about to roll out six or seven obstacles that cumulatively we spent over a million bucks on,” he said. “And these are going to be our secret sauce.” He needs to be careful, he said, “otherwise we’re spending a ton of money just to subsidize everyone else.”

When I asked him about some of the tactics, such as the Facebook messaging that had enraged DeSena, he was more guarded. “Certainly we weren’t trying to do anything that was illegal,” he said, noting that Tough Mudder had targeted fans of other pages, too. But he was hazy on the specifics. “I wasn’t at all involved with the details,” he told me. “Truth be told, I’d have to go back and speak to people in the marketing department at that time and ask them.” The Facebook incident took place in the fall of 2010, when Tough Mudder consisted of Dean, Livingston, and a few interns. One former intern I spoke with snickered at the mention of a marketing department: “Will Dean is the marketing department. None of us made a move without his guidance.”

Still, Dean sounded apologetic, as he did when I brought up the inscribed copy of How to Win Friends and Influence People sent to DeSena. Yet, again he deflected responsibility. “Yeah, OK, um, I’m aware of that,” he said. “That came from our marketing department. There was definitely some frustration at that time with certain members.” (Tough Mudder’s chief marketing officer, Matthew Johnson, emailed me later to explain that Dean had been out of town at the time, so he had written the note for Dean.)

Similarly, the Temecula calendar conflict was an “unfortunate situation” and “there was nothing intentional about any of that”—it’s just the kind of thing that happens in a rapidly expanding company. (Tough Mudder, headquartered in Brooklyn, has gone from nine employees in 2010 to 110 and counting.) “Look, there’s two sides to every story,” he said. “And there are things that we feel would have been in everyone’s best interest if Spartan hadn’t done.” We’d been at it for 45 minutes, and irritation was understandably creeping into his voice. “I think we’ve all grown into quite large organizations quicker than anyone would have anticipated. And I think that there are some things we perhaps didn’t understand and we shouldn’t have done, but that’s true with any business when you’re starting out.”

When I asked about Tough Guy, he cut me off: “We’ve settled with them and that’s all I have to say about that.”

I brought up an incident that occurred just after Tough Mudder launched, when the company ridiculed blogger and ultrarunner Steve Tursi for taking issue with Tough Mudder’s claim that marathons are bad for you. Tough Mudder posted a pic of Tursi on Facebook with a speech bubble that read, “My blog is as interesting as watching a marathon.” Below it appeared this caption: “Steve Tursi Doesn’t Like Us. And we’re not so sure we like him either. He is off to Warrior Dash which is probably where he belongs.”

Dean, sounding increasingly agitated, told me he had emailed Tursi himself to apologize. “You’ve clearly done a hell of a lot of research on us,” he said. “And if we’ve done things in the past that have irritated people, wherever we can we want to make that right. Part of that’s apologizing and admitting when we’re wrong. Unfortunately, when you’re running a business, sometimes people fall out, and I suspect it’s one of those things that will pass.”

The same goes for his feud with DeSena. “We’ll see Joe for a beer in a year’s time,” he told me. “Hopefully we can all laugh about it.”

I RAN MY FIRST Tough Mudder in September 2011, at the Squaw Valley Ski Resort near Lake Tahoe, California. After three miles of slogging through a muddy hell at 7,000 feet of elevation, I encountered the sign that let me know I’d reached the finish line of a Warrior Dash. My first reaction: I have another eight miles of this? But as the subtle ego stroke sunk in, I felt a surge of adrenaline. Here I was, veteran of just a single half marathon, on my way to completing Probably the Toughest Event on the Planet, as the official slogan claims.

Moments like this make you recognize Dean’s irrefutable talent for getting into his customers’ heads. And this, more than anything, is probably the best explanation for Tough Mudder’s success. Dean’s courses aren’t the world’s toughest—both Tough Guy and DeSena’s Death Race break more bones and spirits—but the atmosphere he creates and the courses he constructs somehow make for far more colorful suffering. And, most important, it allows for better storytelling—or “humblebragging.” Having seen dozens of YouTube clips of Electroshock Therapy before my first event, it was the obstacle I feared most. As it turned out, the zap felt more like a whip with a wet towel than the agonizing tasing I’d dreaded. By my second event, at Southern California’s Snow Lake this past summer, I knew I’d hurt more at Arctic Enema, a full-body dunk in a dumpster of neon-colored ice water. At Squaw, the brain freeze had left me feeling like Beetlejuice. Yet I couldn’t wait. Such obstacles endow ordinary people like me with extraordinary tales to fuel cocktail, water-cooler, and Facebook conversations. Even Dean’s fiercest critics concede that he’s a mastermind at spurring this kind of viral messaging. “The truth is that Mr. Mouse, for all his foresight and brilliance, probably couldn’t have pulled off what Dean did,” says Wilson’s old friend and adviser Doug Brodie. “He’s just motivated by different things.”

DeSena reluctantly praises Dean as well. “As much as I hate him, you’ve gotta hand it to the guy,” he said. “He’s smart. Unethical as hell, but smart.”

And hardly content. Tough Mudder is looking to double its reach in 2013, producing 60 events that it expects will draw a million participants. In the not so distant future, “more people will be doing obstacle races and mud runs than will be doing traditional marathons and half marathons,” Dean boldly predicted when I spoke with him.

Of course, even he recognizes that there’s an inherent limit to his company’s growth potential. “We’re not trying to be all things to all people,” he said during his talk at Wix. “We’re not trying to create a nice environment for everyone. It’s a very polarizing brand. You see Tough Mudder and you either say, ‘That looks awful and miserable,’ or you say, ‘That looks awesome. Let me have at it.’ And there isn’t much in between. You either get it or you don’t.”

Scott Keneally (@scottkeneally) lives in Healdsburg, California. This is his first story for Outside.