Dick Costolo of Twitter, an Improv Master Writing Its Script

The audience, le beau monde of cinema, has gathered at the Debussy Theater on this unseasonably cool May morning on the French Riviera. The event, officially the opening of the 2012 Cannes Film Festival, will be remembered for freakish storms that left stars shivering on the soaked red carpet.

But before the Palme d’Or, a little stand-up comedy from Mr. Costolo, the chief executive of Twitter. He has prepared some sober remarks for the occasion — a paean to the mighty tweet, an explication of how new tools of social media are reinventing business, social activism and everything in between.

Nah. Out goes the script.

“Since I’ve got 45 minutes, if we can just start with some quick introductions,” he says, gesturing to the front row. “Start over here. Stand up, say what company you’re from and what animal you could be if you could be any animal.”

So goes his keynote speech at Cannes.

It’s not quite as strange as it sounds. Long before the Twitter revolution and his ascent to the heights of social media, Mr. Costolo was a professional comedian. And you know what? He’s still doing improv — only it’s the business kind. He’ll wax on about growth and revenue like the next C.E.O. But then he’ll dig out a joke and do something that might hurt his business — and miff his investors — because, well, he thinks that something is the right thing to do.

He has broken with the pack on the issue of patent infringement, an issue that drives the tech world crazy, and, in stark contrast to Facebook, has let newcomers to the site opt out of being tracked through the service — a daring move, given that Twitter makes money from advertising.

Even in Silicon Valley, that Neverland of Mark Zuckerberg and hoodied Lost Boy executives, Mr. Costolo can seem an un-C.E.O. To which he says, essentially, whatever.

“People have Plato’s form in their mind of what a leader is, or what a C.E.O. is, and it is a bunch of elements that I really don’t conform to at all,” Mr. Costolo says. “I’ve given this a lot of thought, and I came to the conclusion that I don’t care.”

That kind of attitude could take Twitter to heretofore unimaginable success. Or it could turn it into a B-school case study of a start-up company gone wrong. The choice, for the moment, is Mr. Costolo’s. Today, Twitter seems ubiquitous. But this company didn’t even exist seven years ago. Bankrolled by venture capitalists, it has grown into a multibillion-dollar enterprise with 140 million users worldwide. Although the company doesn’t share its financials, it is estimated that it will have $350 million in revenue this year. “We’re an entire quarter ahead of our projected goals,” one executive says.

Its next big step is to go public on the stock market, and insiders say the current goal is to have an initial public offering in 2014. Twitter’s social media twin, Facebook, has already gone public, of course — and, so far, Facebook stockholders have lost billions, at least on paper. Facebook’s troubled I.P.O. hangs over the technology industry as a cautionary tale of how investors can become star-struck.

Mr. Costolo didn’t found Twitter. Jack Dorsey, Christopher Stone and Evan Williams did. But today Mr. Costolo is essentially running the business alone, and friends and colleagues say he is eager to build the company. And he has succeeded before. During the early 1990s, he worked at Andersen Consulting to subsidize his comedy career. He tried to explain this thing called the World Wide Web to his bosses, but, he says, they didn’t listen. So he and several co-workers started their own consulting firm, Burning Door Networked Media, specializing in Web projects.

Mr. Costolo went on to help found and sell three companies. One of them, Spyonit, notified people when a Web site changed. (This was a decade before anyone had heard the term “real time.”) People used Spyonit to monitor auctions on eBay and to see when comment threads were updated on Web forums. Another of his companies, FeedBurner, helped bloggers syndicate content. FeedBurner was sold to Google in 2007 for more than $100 million.

But starting a small company and then selling it to a big one, difficult as it can be, seems easy next to taking Twitter to the next level. On paper, Twitter is valued at close to $10 billion. That means the most likely exit strategy for its initial backers — notably Charles River Ventures, Benchmark Capital, Union Square Ventures and Mr. Costolo himself — would be to take the company public. But after the Facebook fiasco, Mr. Costolo will have to persuade Wall Street that Twitter, and its share price, could keep rising.

His audience — Wall Street, Silicon Valley and the wider world — is waiting for his next act.