Well, to make a long story short, Jan Koum is Jewish!
Since Jan Koum's mother is Jewish, and in Judaism one's religion is based on one's mother's religion, then that makes him also Jewish. His father is Jewish too.
Jan Koum was born on February 24, 1976 in Kyiv, Ukrainian SSR, Soviet Union.
He is the co-founder and former CEO of WhatsApp, a mobile messaging app which was acquired by Facebook in 2014 for US$19.3 billion.
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