The 2010 TIME 100

If Pandora, the service that allows users to create their own Internet radio stations, is the little music search engine that could, then founder Tim Westergren, 44, is its quixotic engineer. A former rock and jazz musician, Westergren had a big idea in 1999: the Music Genome Project, a typology for categorizing any piece of music according to nearly 2,000 traits identified by Pandora's experts. As a user, you start with, say, a Brian Eno song, then receive a stream of "genetically" related music — Four Tet, Harold Budd and other artists you'll probably like.

For years, Pandora chronically verged on failure. But thanks to the iPhone, 15 million of which carry a Pandora app, it has finally made it over the top — and Westergren and his hybrid of human discernment and digital power are successful as well as cool.

Andersen is a novelist and host of public radio's Studio 360

TIME 100 Social-Networking Index: 8,152