Jan Koum

Jan Koum co-founded WhatsApp and built the most widely used messaging application in history — used by over 2 billion people across 180 countries. Facebook acquired WhatsApp for $19 billion in 2014, making it the largest acquisition of a venture-backed company at the time. The app's success was built on a radical simplicity: no ads, no games, no gimmicks — just fast, reliable messaging that worked on the cheapest smartphones in the world.

Koum's story is one of the most remarkable immigrant entrepreneurship narratives in Silicon Valley history. He grew up in a small village outside Kyiv, Ukraine, in a house with no running hot water. His family immigrated to Mountain View, California, when he was 16. They lived on food stamps. His mother cleaned houses. Koum taught himself computer networking by buying manuals from a used bookstore and returning them after reading them. He got a job at Yahoo as a security engineer and spent nine years there before leaving to build WhatsApp.

WhatsApp's design philosophy reflected Koum's childhood. He grew up in Soviet Ukraine, where the government listened to phone calls. He wanted to build a communication tool that was private, encrypted, and free from surveillance. WhatsApp's end-to-end encryption now protects the communications of 2 billion people. His refusal to build an advertising-supported business model — in a world where nearly every free app monetizes through ads — was a statement of values, not a business strategy. It was the right thing to do, and it turned out to also be worth $19 billion.