There is a sort of practical irreverence about Tough Mudder, the race and the company, which sublets half of an office nearly under the Manhattan Bridge in Brooklyn’s Dumbo neighborhood. Tough Mudder exudes a mix of Gen-Y cool and Harvard-style rootedness, infused with British sensibility and humor.

When Dean looked for a business partner last fall (his Harvard contest teammates scattered to other postgraduate opportunities), he contacted Guy Livingstone, a friend from boarding school.

“We knew each other when our voices broke,” Dean said.

Dean worked for several years for Britain’s Foreign and Commonwealth Office, akin to the State Department in the United States, bouncing around the world in its counterterrorism policy department. Hoping to hone his entrepreneurial spirit — he previously ran a T-shirt operation and a Bollywood poster business — Dean left in 2007 to pursue his M.B.A. at Harvard. He earned it last spring.

Livingstone, meanwhile, felt he was shortchanging his life as a corporate lawyer in London and wanted to stretch his comfort zone. He was learning Arabic in Damascus, Syria, when Dean called. He crossed the ocean to be Tough Mudder’s chief operating officer.

Dean and Livingstone, both 29, seem bent on running a serious business aimed at testing athletes who do not take themselves too seriously. Participants will recite a prerace promise to help others and not whine. On-site artists will ink free Tough Mudder tattoos. Dogfish Head Brewery will provide free beer for a postrace party. Finishers will receive an orange headband, like something seen on a 1970s-era basketball player, that they will be encouraged to wear as a badge of honor.

“But not at work,” Dean said in his usual deadpan. “That’s showing off.”

Dean and Livingstone spent last Thanksgiving weekend touring potential sites, mainly ski resorts and racetracks, within two hours of New York.