Linus Torvalds

Linus Torvalds was just 21 when he changed the world. Working out of his family's apartment in Helsinki in 1991, he wrote the kernel of a new computer operating system called Linux that he posted for free on the Internet — and invited anyone interested to help improve it.

Today, 15 years later, Linux powers everything from supercomputers to mobile phones around the world, and Torvalds has achieved fame as the godfather of the open-source movement, in which software code is shared and developed in a collaborative effort rather than being kept locked up by a single...