Jan Koum

Jan Koum cofounded WhatsApp, now the world's biggest mobile messaging service, in 2009.

Facebook bought the startup for $22 billion in cash and stock in 2014.

He resigned as CEO of WhatsApp in April 2018 and announced he would leave Facebook's board as well.

Koum worked at Yahoo for nearly nine years before leaving to found WhatsApp.

Koum has donated $1.15 billion of Facebook stock to charitable entities, including to his Koum Family Foundation.