CHICAGO -- It's not uncommon for Gian Fulgoni to be told how much he looks like Dustin Hoffman, or even to be mistaken for the Academy Award-winning actor and pressed for an autograph.

It happens at least once a week. When it does, the typically gregarious, outgoing Fulgoni, whose first name is pronounced Jan, will smile politely, shake his head and move on.

"Do you think I've never heard that before?" he asks rhetorically. "Why do you feel a need to tell me that when you don't know me?"

But his wife, Sarinda, points out that sometimes -- typically at one of the 40 to 50 conferences where he speaks each year -- people approach Fulgoni, 64, to ask, "Hey, are you Gian Fulgoni?"

After 40 years in market research and now executive chairman of comScore, Fulgoni is well known as an online-data guru who can crunch numbers, articulate the results and build businesses around the combination.

If you've heard a statistic about how consumers act online -- say, where they like to buy airline tickets, or what websites they frequent for clothes shopping -- chances are good it came from Fulgoni and the database he's built with his team at comScore.

The firm's data can influence what kind of discounts online retailers offer during the holiday shopping season, or what kind of ads shoppers see as they browse the Web for back-to-school deals. ComScore data crowned social-media darling Pinterest as the fastest independent website to reach 10 million unique visitors in one month.

After bruising comments by General Motors about the effectiveness of Facebook advertising, the tech company commissioned comScore to prove that marketing on the site really does have an impact on sales.

A publicly traded company based in Reston, Va., and employing nearly 100 in Chicago, where Fulgoni is based, it also provides data and software to measure and analyze consumer behavior online and off.

"Publishers, advertisers and agencies in the middle -- those are our three constituencies, and their interests are not always aligned," he said.

Fulgoni started figuring out in college that he had a knack for translating difficult concepts into widely understandable language. Studying physics, he noted that his brilliant professors couldn't communicate well. They didn't assign textbooks, so students who were slow taking notes, missed lectures, or just didn't understand were simply out of luck.

He also saw an emerging trend: the rise of data.

"We're in a day and age where it's all about big data," he said. "Nerds are the new heroes."

Fulgoni started comScore in 1999 with Magid Abraham, his former employee at Information Resources Inc. (IRI), the market-research firm where he was president and later CEO for nearly 18 years.

Now, Fulgoni and Abraham are known as the yin and yang of comScore. While Abraham figures out the technology, Fulgoni is the storyteller who interprets data and communicates it to clients and the public.

"Maybe I'm fortunate in that I can combine right brain and left brain," Fulgoni said.

When he's in town -- he has racked up millions of airline miles on the job -- Fulgoni works out of a bright, spacious office on the 34th floor of Chicago's Willis Tower with large windows that provide an expansive view of Lake Michigan. It's speckled with his beloved Pittsburgh Steelers paraphernalia.

Like many top executives, Fulgoni is known for his relentless schedule and workaholic tendencies. But he's also known for really enjoying what he does. His enthusiasm for data and market research, according to colleagues, is infectious.

"Gian is very persistent: He does not take no for an answer," Abraham said. "He's very intellectually curious, and he's going to debate you and understand where you are coming from. As a result, he's also somebody who flattens obstacles out of the way to make sure things happen."

That includes going head to head in a more than 30-year battle with archrival Nielsen, first at IRI and now at comScore.

Fulgoni grew up in Wales, where his father ran a restaurant. Majoring in physics at the University of Manchester in the late '60s, Fulgoni knew he was good with numbers, but figured to have a competitive advantage, he had to have something else. So in graduate school at Lancaster University, he took up marketing.

After grad school, Fulgoni landed his first data job at Management Science Associates in Pittsburgh, which he considers his first U.S. hometown. In a decade he rose to become an executive vice president and manager of the firm's Chicago office.

In 1981 he was recruited as president of Information Resources Inc., which made its name on capturing consumer data from retailers through a bar-code scanners. In 1989, he was tapped to be CEO.

"Gian's a real instigator," said Jack Honomichl, founder of Inside Research, a market-research trade publication and author of the Honomichl Global Top 25 Research Report.

"He stirs things up and gets things going," Honomichl said referring to Fulgoni's ability to predict what retailers need and how to gear their business toward it.

But by the late '90s, investors weren't happy with the direction of the company's stock and wanted a change in the executive suite. In 1998, Fulgoni stepped down as chairman.

In the meantime, he had been mulling how to tap into the Internet boom. "You had to be asleep to not realize what the Internet was doing," he said.

Sitting in his house in Florida, he set about writing a plan for doing what IRI did, but on the Web. In those days, he said, no one was measuring e-commerce.

The company started by offering consumers incentives such as software that speeds up their Internet connections to persuade them to let their computers be monitored. From the data comScore mined, it was able to provide Web publishers and advertisers with valuable information about consumers online.

It was the height of the tech bubble, and as a veteran, Fulgoni found that investors were eager to pour money into his idea.

Then the bubble burst. Fulgoni's fledgling company had to recalibrate.

"We were starting to see revenue, and along came these tsunamis that severely dampened corporate demand for our services," he said.

But Fulgoni had the confidence that he and Abraham had created something special.

"We were pushing back a lot of frontiers, doing stuff that hasn't been done before," he said. "That's pretty energizing."

In time, comScore expanded to include monitoring shopping behavior offline too, aiming to give marketers and Web publishers a full picture of what consumers were thinking, doing and buying.

Fulgoni has a litany of advice for up-and-coming entrepreneurs: Find a brilliant team. Be flexible. There's no substitute for hard work. And don't get locked into one business plan.

"The speed at which things are changing is a two-edged sword," he said. "Every day you wake up and there's something new that's a threat or an opportunity."