A few years back, Peretti produced something that went viral. He challenged himself to do it again. And he did. Then, nobody thought you could engineer viral, but Peretti saw the power of social publishing clearer than anybody else. "I've spent over a decade thinking about how ideas spread," he said at South by Southwest this year. Indeed, the Web has morphed from a portal and search-driven marketplace to a medium dominated by social content. And under Peretti's leadership, BuzzFeed has proven that online publishing can mix the smart and serious (witness its political and business coverage) with the extremely light. It's tapped into a Gen Y Web culture that few in traditional media have managed to via its particular brand of commentary, GIFs and, of course, all those lists. Peretti's not an editor in the traditional sense—and yet, it is his editorial vision that is setting the agenda for the modern Web.