He revealed his departure in a Facebook post, saying that he would take some time off before contemplating his next move. Koum and Brian Acton co-founded WhatsApp in January 2009, and Facebook’s $19 billion acquisition of the messaging app officially closed in October 2014.
Koum is also a member of Facebook’s board of directors, and he informed Facebook that he will not stand for re-election at the company’s 2018 annual meeting.
Acton left Facebook and WhatsApp last September to start a nonprofit, and he and computer security researcher Matthew Rosenfeld, also known as Moxie Marlinspike, started the Signal Foundation in February to develop open-source privacy technology.
Facebook CEO Mark Zuckerberg announced during the company’s 2017 Q4 earnings call that WhatsApp had surpassed 1.5 billion monthly users.
Zuckerberg replied to Koum’s Facebook post announcing his departure: “I’m grateful for everything you’ve done to help connect the world and for everything you’ve taught me, including about encryption and its ability to take power from centralized systems and put it back in people’s hands. Those values will always be at the heart of WhatsApp.”