Only 5 People Are Richer Than Zuckerberg Now His fortune surpassed the Koch brothers' on Thursday By Michael Harthorne, Newser Staff Posted Jan 28, 2016 6:10 PM CST 11 comments Comments Facebook CEO Mark Zuckerberg officially became the world's sixth-richest person on Thursday. (AP Photo/Paul Sakuma, File) (Newser) – Facebook CEO Mark Zuckerberg returned from paternity leave this week, NBC News reports. As a welcome-back gift, he officially became the world's sixth-richest person on Thursday. According to Bloomberg, his net worth increased by $6 billion on the stock market Thursday, lifting him past the Koch brothers. The 31-year-old is now worth $47.5 billion. He's currently behind only Bill Gates ($77.9 billion), Amancio Ortega ($70.2 billion), Warren Buffett ($59.1 billion), Jeff Bezos ($51.9 billion), and Carlos Slim ($48.6 billion). But those five have all lost money this year to the tune of a combined $19 billion. The news prompted CNN to raise the possibility that Zuckerberg "might be the best CEO in America." Facebook is less than 12 years old but is worth more than $300 billion. The $1 billion it paid for Instagram "has turned out to be an amazing bargain." And it's seemingly mastered mobile, with 80% of its ad revenue coming from that sector. According to Bloomberg, Facebook announced Wednesday that sales were up 52% in the fourth quarter and it had more than doubled its net income over the previous year. NBC points out Zuckerberg has promised to give most of his fortune away.