WhatsApp Inc. was founded in 2009 by Americans Brian Acton and Jan Koum, Both former employees of Yahoo!
Back in 2009, Brian Acton sent out the following tweets after going for a job at Twitter & Facebook
“Got denied by Twitter HQ. That’s ok. Would have been a long commute” @brianacton 24 May 2009
“Facebook turned me down. It was a great opportunity to connect with some fantastic people. Looking forward to life’s next adventure.” @brianacton 4 Aug 2009
So He and Jan Koum, a Colleague from Yahoo, set out to do their own thing, WhatsApp.
& Today, they sold that thing to Facebook for 19 Billion dollars..