At the age of 18, Koum showed his interest in programming and joined San Jose State University and simultaneously worked at Ernst & Young as a security tester. He was appointed by the CEO of Yahoo to work as an infrastructure engineer in 1997, shortly after he met Brian Acton while working at Ernst & Young as a security tester. He worked at Yahoo for more than nine years.
In 2007, Koum left his job at Yahoo and traveled around South America. After a year, he applied to work at Facebook along with his friend Brian Acton, however, they failed to get the job at Facebook.
The idea to develop an app struck Koum soon after he bought an iPhone that had a pre-installed app store. Consequently, he discussed his idea of Whatsapp with his friend Alex Fishman over a tea. After a week, on his birthday, he formed WhatsApp Inc. in California. Just a month later, his apps caught Facebook's attention.
After that, the founder of Facebook, Mark Zuckerberg contacted Koum in the spring 2012 and called him at a coffee shop in Los Altos, California. Then the duo began a series of dinners and walks in the hills above Silicon Valley.
On February 9, 2014, Koum was called by Zuckerberg to have dinner at his home and asked him to join the Facebook board. 10 days later, Facebook made an announced regarding the possession of WhatsApp. Facebook reportedly bought it for US$19 billion.
Apart from these, Koum has also been showing his involvement in political activities. On February 27th, 2018, Koum showed his support for the re-election of Donald Trump. However, he hadn't spoken about his support for the 2016 presidential campaign of Donald Trump.
Moving on his personal aspects, Koum is an American by nationality and belongs to white ethnicity. He is married to his longtime girlfriend, Evelina Mambetova, a Ukrainian Model. He lives a happily married life with his wife and there are no conflicts between the couple that signifies divorce in future. Likewise, there is no news regarding their children. It seems they have not made up their mind to welcome any.
In 2014, Koum was listed as 62nd richest people in the world by Forbes with the estimated net worth of $7.5 billion. He is also involved in charitable work and has donated one million dollars to The FreeBSD Foundation and $556 million to the Silicon Valley Community Foundation. As per some online sources, his current net worth is estimated to be $8.9 billion.