John and Patrick Collison, 28, 29
The Irish-born brothers are a couple of the world’s youngest self-made billionaires. Patrick and John dropped out of MIT and Harvard, respectively, and sold their first business—an online auction management company—for a reported $5 million in 2008. Then they embarked on the idea that would become Stripe, now a payments behemoth valued at $9.2 billion. The company processes tens of billions of dollars in digital commerce transactions each year, inking deals with the likes of Amazon, Lyft, and Facebook.
40 Under 40