At age 20, high-school dropout and startup industry veteran David Karp co-founded Tumblr, the now six-year-old blogging platform that was just bought by Yahoo for $1.1 billion. But who is he? The New York Times profiles Karp, who left school at age 14 to focus on programming and web design and worked on several projects before striking gold with Tumblr. Fellow Tumblr co-founder Marco Arment, meanwhile, looks back on his time working with Karp, saying the acquisition by Yahoo may be a great thing for Tumblr. "Tumblr is David, and David is Tumblr," he says. "We — internet users, creative people, publishers, socializers — will be much better served if David can focus on his product's features, design, and messaging instead of worrying about server architecture and raising more money."