Zadeh, the son of Iranian immigrants, got a Ph.D. in bio­engineering but fell in love with product design after learning to use Photoshop. In 2010 he found his way to the then-nascent home-sharing startup, where he joined as the ninth employee. Today “Joebot,” as he’s known around the office, leads product efforts for the company, which hit 100 million users this summer. Up next, Airbnb plans to help guests experience more than just a local roof, and Zadeh’s job as the “conductor” of Airbnb’s apps and website will be more important than ever.