By ensuring vaccines are invented and distributed, Bill Gates says, his foundation is dramatically reducing the number of childhood deaths in poor countries. Marie McGrory/NPR hide caption

Satya Nadella, Microsoft's next CEO. Stephen Brashear/AP hide caption

Satya Nadella, who's reportedly in line to be Microsoft's next CEO. Stephen Brashear/AP hide caption

Bill Gates at an event held by his foundation in Berlin last November. Maurizio Gambarini /EPA/Landov hide caption

One experimental condom has tabs on either side so it's easier to put on in the dark. Courtesy of California Family Health Council hide caption

Those are the hands of David Bradley, an original member of the IBM PC team and the inventor of the control-alt-delete function, hitting the right keys. Bob Jordan /AP hide caption

Larry Ellison, CEO of Oracle, is No. 3 on the Forbes 400 list of the wealthiest Americans. Stephen Dunn/Getty Images hide caption

Microsoft CEO Steve Ballmer speaks at the Microsoft "Build" conference in San Francisco in June. Robert Galbraith /Reuters/Landov hide caption

There's no better deal than getting polio cases down to zero, philanthropist Bill Gates says. Marie McGrory/NPR hide caption

This handshake between South Korean President Park Geun-hye and Microsoft founder Bill Gates sparked debate over whether the American — who kept his left hand in his pocket — had been rude. Other photos clearly show Gates' hand in his pocket.0 Lee Jin-man/AP hide caption

An estimated 15 billion condoms are manufactured each year and 750 million people use them. ederk /iStockphoto.com hide caption

Bill Gates, co-founder of the the Bill & Melinda Gates Foundation, checks out a toilet demo at the Reinvent the Toilet Fair in Seattle, Wash. The festival featured prototypes of high-tech toilets developed by researchers around the world. Bill & Melinda Gates Foundation hide caption