Jan Koum is a Ukrainian-American entrepreneur best known as the co-founder of WhatsApp, a popular messaging application. Born on February 24, 1976, in Fastiv, Ukraine, he immigrated to the United States with his mother in 1992. Koum worked at Yahoo for nearly a decade before starting WhatsApp in 2009 with Brian Acton. Under Koum's leadership, WhatsApp grew rapidly, reaching over 2 billion users worldwide. In 2014, Facebook acquired the app for approximately $19 billion, making it one of the largest tech acquisitions in history. Koum served as the CEO of WhatsApp until 2018, focusing on user privacy and security.