Who co-founded WhatsApp with Jan Koum?

Brian Acton co-founded WhatsApp with Jan Koum.

The two founders met while working in the late 1990s and later spent about nine years together at Yahoo!. After leaving Yahoo! in 2007, they traveled and explored new opportunities. Both reportedly applied for jobs at Facebook but were rejected, before building the messaging company that would eventually become one of the world's largest communication platforms.

Koum incorporated WhatsApp Inc. in California on February 24, 2009. Acton joined the project soon afterward and helped secure $250,000 in seed funding from former Yahoo! colleagues. That contribution led to Acton receiving co-founder status and an ownership stake in the company.

Facebook announced its acquisition of WhatsApp in February 2014 for a deal valued at roughly $19 billion. Acton left WhatsApp in 2017 and later helped establish the Signal Foundation. The other choices are associated with Instagram or Facebook, not WhatsApp's founding.