In 2009, Jan Koum founded WhatsApp, the world's largest mobile messaging app. Ranking #60 on the Forbes 400, Mr. Koum is worth $7.5 billion. Last year he donated $560 million, or 7.5 percent of his worth, to the Silicon Valley Community Foundation to set up a donor-advised fund. His fund issued a grant to FreeBSD, a free open-source operating system project.

Albert Gea/Reuters/File
WhatsApp Chief Executive Officer and co-founder Jan Koum holds up a mobile phone as he delivers a keynote speech in February, 2014.