Bill Gates: The Rolling Stone Interview

At 58, Bill Gates is not only the richest man in the world, with a fortune that now exceeds $76 billion, but he may also be the most optimistic. In his view, the world is a giant operating system that just needs to be debugged. Gates' driving idea – the idea that animates his life, that guides his philanthropy, that keeps him late in his sleek book-lined office overlooking Lake Washington, outside Seattle – is the hacker's notion that the code for these problems can be rewritten, that errors can be fixed, that huge systems – whether it's Windows 8, global poverty or climate change – can be improved if you have the right tools and the right skills. The Bill & Melinda Gates Foundation, the philanthropic organization with a $36 billion endowment that he runs with his wife, is like a giant startup whose target market is human civilization.

Personally, Gates has very little Master of the Universe swagger and, given the scale of his wealth, his possessions are modest: three houses, one plane, no yachts. He wears loafers and khakis and V-neck sweaters. He often needs a haircut. His glasses haven't changed much in 40 years. For fun, he attends bridge tournaments.

But if his social ambitions are modest, his intellectual scope is mind-boggling: climate, energy, agriculture, infectious diseases and education reform, to name a few. He has former nuclear physicists helping cook up nutritional cookies to feed the developing world. A polio SWAT team has already spent $1.5 billion (and is committed to another $1.8 billion through 2018) to eradicate the virus. He's engineering better toilets and funding research into condoms made of carbon nanotubes.

It's a long way from the early days of the digital revolution, when Gates was almost a caricature of a greedy monopolist hell-bent on installing Windows on every computer in the galaxy ("The trouble with Bill," Steve Jobs once told me, "is that he wants to take a nickel for himself out of every dollar that passes through his hands"). But when Gates stepped down as Microsoft CEO in 2000, he found a way to transform his aggressive drive to conquer the desktop into an aggressive drive to conquer poverty and disease.

Now he's returning to Microsoft as a "technology adviser" to Satya Nadella, Microsoft's new CEO. "Satya has asked me to review the product plans and come in and help make some quick decisions and pick some new directions," Gates told me as we talked in his office on a rainy day a few weeks ago. He estimates­ that he'll devote a third of his time to Microsoft and two-thirds to his foundation and other work. But the Microsoft of today is nothing like the world-dominating behemoth of the Nineties. The company remained shackled to the desktop for too long, while competitors – namely, Apple and Google – moved on to phones and tablets. And instead of talking in visionary terms about the company's future, Gates talks of challenges­ that sound almost mundane for a man of his ambitions, like reinventing Windows and Office for the era of cloud computing. But in some ways, that's not unexpected: Unlike, say, Jobs, who returned to Apple with a religious zeal, Gates clearly has bigger things on his mind than figuring out how to make spreadsheets workable in the cloud.