8. Jan Koum
Jan Koum was born in a small Ukrainian village. He immigrated to the U.S. at age 16, living on food stamps and sweeping floors. He taught himself programming and got a job at Yahoo. After years of hardship, he co-founded WhatsApp in 2009. Facebook later acquired it for $19 billion. Koum’s journey from poverty to tech billionaire is one of Silicon Valley’s most inspiring.