It's the end of an era for Tumblr fans. David Karp, Tumblr's founder, has resigned from his CEO position after 11 years at the job. The company's operations chief, Jeff D'Onofrio, is taking the reins. Karp didn't go into detail about his reasons for leaving, but he told his team that the move came after "months of reflection" about his personal goals. We've asked Tumblr if it can comment beyond Karp's own statements.