Jan Koum

WhatsApp; engineering-scale essays (early Erlang stack)

Jan Koum co-founded WhatsApp in 2009 and served as its CEO until 2018, overseeing its acquisition by Facebook for ~$19 billion in 2014. He built WhatsApp's server infrastructure on Erlang, enabling the platform to handle billions of messages with a famously lean engineering team. Koum has been a vocal advocate for end-to-end encryption and user privacy.