(FORTUNE Magazine) – While Microsoft's chairman and co-founder is no longer CEO, he remains the world's richest man (estimated net worth: well over $30 billion)--and as chief software architect, he wields enormous power over how our computers behave. But it is his business acumen that gives Gates, 47, the most clout. More than anyone, he changed the economics of IT by creating software and hardware standards that transformed computers into commodity products. Along the way he achieved an effective monopoly in Microsoft's primary business of operating systems software, and he weathered the most aggressive federal antitrust challenge in decades. Now he's out to change the world another way: by throwing billions at eradicating infectious diseases. --Brent Schlender