I worked on a number of projects that were used by millions of people and that also served as inspiration to what we now call "crowd-sourcing."

Before the Internet, coordinating more than 100,000 people, let alone paying them, was essentially impossible. But now with the Internet, I've just shown you a project where we've gotten 750 million people to help us digitize human knowledge.

I co-founded Duolingo with the mission of bringing free language education to the world.

I watch a lot of TV. That's how I spend most of my time outside of work. If I had more time, I would fill it 100 percent with watching TV.

Together with my advisor, Manuel Blum, I co-invented CAPTCHAs, or computer-generated tests that humans are routinely able to pass but that computers have not mastered (they are the squiggly computer letters that are prevalent across the web).

People are good at figuring out what's attractive, and computers are good at quickly searching and finding. You put them together, and bang!

I worked on a number of projects that were used by millions of people and that also served as inspiration to what we now call "crowd-sourcing."