Fortune Magazine -- Google (Charts) relishes being secretive and opaque, the better to confuse the competition, and one of the company's biggest mysteries is its leadership triumvirate. Figuring out what exactly it is that these three guys do is a Silicon Valley parlor game. Beyond the technology world, the trio's individual attributes are even murkier, with some having heard only a little about the middle-aged guy, Eric Schmidt, and not being able to distinguish at all between co-founders Larry Page and Sergey Brin, often called, even by those who know them well, "the twins."

The two co-founders often are indeed difficult to separate. They spend huge amounts of time together, and have similar management quirks. Both, for instance, recently stopped using administrative assistants, choosing instead to keep their own calendars and answer their own messages, just like other 32-year-old businesspeople. It's unclear if the new approach will make them more punctual. They're both infamous for being unwilling to commit to appointments, often blowing them off altogether. They have their differences, of course. Here's how they and their avuncular CEO divide their responsibilities.

Disorderly conduct: Page and Brin (wearing goofball lab smocks) and CEO Schmidt in the middle

More from Fortune Leading during a downturn There are still too many houses The race to own mobile advertising FORTUNE 500 Current Issue Subscribe to Fortune

Eric Schmidt, chairman and CEO. Conventional wisdom is that Schmidt's job is to break ties between Page and Brin and to communicate with Wall Street and the news media. Insiders say that underplays his role. He sets the company's overall agenda, gives direction on workaday issues the co-founders don't care to address, and more than occasionally reminds Page and Brin to behave themselves. Schmidt also is becoming a power in Silicon Valley, having recently joined the board of Apple (Charts), the other buzziest company.

Larry Page, president, products. Acknowledged as the thought leader of the company and co-founder most likely to roll up his sleeves and make sure things get done. Page, who carries résumés home in a plastic bag on the weekend so he can review them before the week starts, is known for a short temper and great attention to detail -- yes, the latter is a nice way of saying "micromanager". He was Google's CEO until Schmidt arrived in 2001, and many assume Page intends to be chief executive again someday.

Sergey Brin, president, technology. Mr. Outside to Page's Mr. Inside, Brin is responsible for advertising initiatives -- the moneymaking part of Google -- as well as overseeing business deals. He's considered more laid-back than Page and is known for being more intuitive and less emotional. Brin can chew up hours discussing which flat-panel TV he should buy. He's also been pushing hard for Google to streamline its product offerings, which officially is Page's purview.