YouTube’s CEO since early 2014, Wojcicki has worked to turn the massive video site into a viable business. Now that half of YouTube’s views come from mobile devices, she has revamped its mobile app. With some $4 billion in revenue, YouTube delivers only a small fraction of Google’s overall $71.5 billion in sales, but it is growing fast as it recruits content creators and advertisers to compete with an increasingly aggressive Facebook. Under Google’s recent restructuring, Wojcicki now reports to new CEO Sundar Pichai.