Net worth: $85.2 billion

Age: 61

Country: US

Industry: Tech

Source of wealth: Self-made; Microsoft

At just 20, Bill Gates cofounded Microsoft with his childhood friend Paul Allen. Months before his 31st birthday, the company went public, making Gates a billionaire. He served as CEO of the software titan until 2000 and was its chairman and largest shareholder until 2014. Though he still sits on the company's board, Gates is no longer actively involved in Microsoft.

Gates is not only the richest man in the world — his net worth increased by $10.6 billion in the last year alone — but he's also the most generous. Since 1999, Gates and his wife have helmed the Bill & Melinda Gates Foundation, one of the most powerful charities in the world. The foundation — which controls an endowment of more than $40 billion — aims to lift millions of people out of poverty, with a heavy focus on eliminating HIV, malaria, and other infectious diseases. The couple is also working on a plan to bring mobile banking to the 2 billion adults who don't have a bank account. 

He's also cofounder of the Giving Pledge, which he launched in 2010 with good friend and fellow billionaire Warren Buffett as a promise to donate 50% or more of their fortunes. The Giving Pledge now counts Mark Zuckerberg and Elon Musk among its 156 members.