Jan Koum — WhatsApp

Koum grew up in a village outside Kyiv, Ukraine, with no hot water and a party-line telephone. He immigrated to Mountain View at 16, lived on food stamps, and dropped out of San Jose State. He and Brian Acton built WhatsApp with 55 employees — no marketing, no ads, no games. Facebook bought it for $19.3 billion in 2014, the largest acquisition of a venture-backed company in history. A kid on food stamps built a $19 billion company with 55 people. That's not a Silicon Valley fairy tale; it's the most improbable success story in tech history.