In April 26, 1986, 10-year-old Max Levchin and his family were living in Kiev, Ukraine - 90 miles south of the Chernobyl nuclear power plant. While the Soviet government scrambled to cover up the scale of the disaster, Levchin's mother, a physicist, understood the radiation risk and immediately packed Max and his brother off to live with his grandmother in Crimea, hundreds of miles away. Five years later, the family arrived in Chicago as Jewish refugees with just $700; the ruble had collapsed and the government had limited how much money people could take out of the country.

"Part of the experience coming to the U.S. from a socialist country is that I just wasn't prepared for a lot of the things that existed here, good and bad," Levchin says. "I got my first credit card a couple years after coming to America and promptly destroyed my credit, because I had no idea how to use this power tool." He's speaking on January 13, the day Affirm Holdings - the buy now, pay later fintech Levchin cofounded and runs as CEO - went public. Its shares doubled that day to $96, making the company worth $24 billion and his stake worth $2.5 billion.