Mr. Rubin was a founder of Android, the mobile operating system behind Google’s smartphones and tablets, which Google acquired in 2005. The product was introduced in 2007 to rival the iPhone, and today has more than one billion active users. Last year, Mr. Rubin left Android and began an ambitious acquisition spree that included at least eight companies, with the intent of building a robotics business inside Google. The division is focused on a diverse set of areas surrounding manufacturing and logistics. For instance, Mr. Rubin told people that he intended to embark on a 10-year project that would automate things like Google Express — the company’s same-day delivery service. Mr. Rubin is now leaving to start a tech incubator focused on start-ups interested in building hardware. Mr. Rubin’s departure is part of a series of recent executive moves that seem to give Mr. Page more room to focus on the company’s longer-term bets — like robotics — while handing almost all the responsibility for Google products to Sundar Pichai, a rising star.