Azim Premji among world's 10 richest tech titans

None of the actual robots featured in this year's E-gang (our annual roundup of tech innovators) are likely to become billionaires, but some of the inventors-cum-entrepreneurs behind the next generation of robotic assistants might.

After all, great innovation is often rewarded with great wealth.

The world's ten richest technology billionaires have a collective net worth of $174.2 billion, or more than the gross domestic product of Israel. Bill Gates, worth $50 billion, has been the world's richest man for 12 consecutive years. Even the poorest in the group, SAP co-founder Hasso Plattner, with an estimated net worth of $6.4 billion, ranks among the hundred richest people on the planet. (All net worth estimates are from the most recent issue of The World's Billionaires.)

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Inarguably these men--and yes, they are all men--have changed the world. Some of the companies they founded--Microsoft , Oracle , SAP, Dell --form the foundation of the working day for millions of office workers.

Others--Google, eBay--have transformed everyday activities like shopping and searching the Internet. Not only have they themselves become rich, but countless individual investors have enriched themselves by riding on their coattails.

But their restless entrepreneurial energy hasn't been confined to their companies. Three of the ten--Plattner, Paul Allen and Pierre Omidyar--aren't even actively involved in the companies they founded.

Allen is at the centre of a dizzying array of activities. He was the sole investor in SpaceShipOne, which won the X-Prize for the first privately funded trip to suborbital space in October 2004. He has funded everything from the Search for Extraterrestrial Intelligence to a museum devoted to the history of rock.

He owns both the Seattle Seahawks and the Portland Trailblazers, and maintains dozens of investments in everything from energy to cable television to movie studios. His Paul G. Allen Family Foundation gives away tens of millions annually to nonprofit organizations in Seattle and Washington state.

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Omidyar, who started eBay in 1995 but leaves the site's day-to-day operations in the hands of fellow billionaire Meg Whitman, also spends his time giving away his money. With his wife, Pam, he runs the Omidyar Network, which funds an eclectic range of projects, both nonprofit and for-profit. Investments cover the spectrum, from women's rights and microfinance to open-source software and Digg.com.

Plattner, the professor who co-founded SAP, is officially retired from the software giant. But he keeps his hands in the business world through his HassoPlattnerVentures, which invests in and nurtures young information and technology companies in an effort to "reawaken the entrepreneurial spirit in Germany."

In June, Gates announced that he too is moving away from the corporate world. As of July 2008, he will no longer be a full-time employee of the company he founded 31 years ago. Although he will continue to serve as Microsoft's chairman and advise the company on key projects, Gates will devote the majority of his time to philanthropy through the Bill & Melinda Gates Foundation.

Not coincidently, only weeks after Gates said he was transitioning out of Microsoft, Warren Buffett, the world's second-richest man, announced that he intended to give the bulk of his $42 billion fortune to the Gates' foundation.

Even tech titans that remain involved in their companies often pursue second lives outside of the office. Larry Ellison, who founded database giant Oracle in 1977 and remains its CEO, recently told Forbes: "Life is short. I'm not going to spend every minute of it with Oracle."

In fact, Ellison doesn't even maintain an office at Oracle's Silicon Valley headquarters. Yachting remains paramount among his myriad outside interests. He owns a 450-foot yacht and is the prime force behind BMW Oracle Racing, the challenger of record for the 2007 America's Cup.