Every now and then, when he’s spoiling for a fight, Travis Kalanick has a face like a fist. At these times, his eyes crinkle, his nose flares, and his mouth purses just like a clenched hand readying a punch. Even his Marine-style, salt-and-pepper hair seems to stand on end and bristle, as it were, at whatever the 38-year-old entrepreneur happens to be facing down. And as the C.E.O. of Uber, the five-year-old ride-sharing juggernaut that in June was valued at $18.2 billion by investors, Kalanick has found no shortage of foes.

He has directed barbs—in speeches and videos, and on Twitter—especially fervently toward the taxi industry, but also toward city and local regulators across the country (and now the world), his rivals, and sometimes even his own customers when they dare to question his company’s practices.

But is it real? Sort of and yet not so much, as it turns out. As one venture capitalist who has worked with Kalanick says of him: “It’s douche as a tactic, not a strategy.”

In fact, in many ways, Kalanick wears the characterization almost as a badge of honor—proof of his zeal and dedication to his mission: to drastically disrupt what he considers a very broken transportation system. “Look, I’m a passionate entrepreneur. I’m like fire and brimstone sometimes. And so there are times when I’ll go—I’ll get too into the weeds and too into the debate, because I’m so passionate about it,” he says.

One of Uber’s earliest investors explains Kalanick’s pugnacious reputation in more matter-of-fact terms: “It’s hard to be a disrupter and not be an asshole.”

As the fairy tale goes, Uber was born on a snowy night in Paris in 2008, when Kalanick and his friend Garrett Camp could not get a cab. The two vowed then and there to solve the problem with a revolutionary new app. The premise was dead simple: push a button and get a car.

It’s a tasty blame-the-French origin story, but it is only partially true. The pair were in Europe, attending LeWeb, an annual European tech conference. Both were flush with cash and on the hunt for their next business idea. Kalanick had recently sold his second start-up, Red Swoosh, a content-delivery company, for $20 million to Akamai Technologies. Camp had sold his company, StumbleUpon, a Web discovery engine, to eBay for $75 million the previous year.

Back in their shared apartment on the outskirts of Paris, in a session that Kalanick had called the JamPad, they got to talking with some other entrepreneurs about start-up ideas. Among the many schemes bandied about was the notion for an on-demand car-service app, inspired by their frustration in the snow. Those who were in the room, however, said the concept that would become Uber did not stand out over other ideas discussed that evening.

After getting back to San Francisco, Kalanick pretty much moved on from the idea. But Camp did not, obsessing over the concept of a car service, so much so that he bought the domain name UberCab.com.

Camp, who owns a large chunk of Uber, says he could not let the idea go and wanted to partner with Kalanick. In Paris, the pair had climbed to the top of the Eiffel Tower, during which Kalanick had hopped over barriers to get a better view. “I liked that quality of going for it,” recalls Camp. “I knew such a big idea would take a lot of guts, and he impressed me as someone who had that.”

“He said, ‘Do you want to run a limo company?,’ and I’m like, ‘I don’ t want to run a limo company,’ ” says Kalanick, who credits Camp with the vision for what would become Uber. When he looks back on his initial reticence now, Kalanick explains it as situational. He was depressed after his first start-up failed badly and his second went largely sideways. He was, as he recalls, deeply afraid of failure. “I had gone through eight years of real hard entrepreneuring. I was burned. So, I just wasn’t ready yet,” says Kalanick. In fact, he had been living at home with his parents in his childhood bedroom not long before his trip to Paris, after those two start-ups had failed to flourish. He had dropped out of U.C.L.A. nearly a decade earlier to become a tech founder. And, at just over 30, he was practically middle-aged by Silicon Valley standards.