The 2008 TIME 100

Think it's hard to keep the computers in your kid's school up-to-date? How about the 50% of children worldwide who learn outdoors? If half the planet was not going to be excluded from the Internet age, somebody had to come up with a machine that would work in such unlikely places. Mary Lou Jepsen, 43, did. Along the way, she also survived a terrifying disease.

Jepsen is a veteran of the MIT Media Lab, where she co-created the world's first holographic video system in 1989—back when computer imaging meant straight lines on a cathode screen. In 2005 Jepsen and Media Lab founder Nicholas Negroponte launched the nonprofit, open-source One Laptop Per Child program, which, as the name suggests, was an attempt to get a computer to every child in the world who needs one. The machines would have to work in extreme climate, amid spotty power and Internet connectivity, and be readable in direct sunlight. Oh, and they would have to sell for around $100 each. Negroponte ran the project, but Jepsen was the lead innovator and architect of the hundreds-strong team that would design the machine.

Within two years they succeeded, creating a computer that can run on solar power, with five times the screen resolution of other laptops and a wireless system that creates its own network. The $100 price point has not been met, but $188 has. Jepsen did all that 12 years after receiving a diagnosis of a brain tumor in 1995 that had gone undetected for five years. She beat the disease but must take a dozen pills every day to keep her hormone output stable. Something of a self-taught expert on hormones, she now offers her insights to others who are diagnosed with the same illness. Jepsen is known among her friends as the "light lady" for her work with computer imaging. But the kind of light she's shedding goes far beyond the screen.

Kahle is director and co-founder of the Internet Archive, an open, online library for historical collections