Jan Koum, Facebook Inc. director and co-founder of its WhatsApp unit, is leaving the messaging service after what people familiar with the matter described as disagreement over putting advertising on its app and frustration over the confines of working in a big company.
Mr. Koum, who was chief executive of WhatsApp, gave no reason for leaving in a Facebook post on Monday about his departure. The move follows the departure last year of fellow WhatsApp co-founder Brian Acton, who has since been publicly critical of the social-media giant. The two men, both privacy advocates who started their encrypted messaging app nearly a decade ago, joined Facebook after it acquired WhatsApp in 2014 for $22 billion, making them both billionaires.
Mr. Koum’s departure followed an internal debate over whether to put advertising in WhatsApp, a move that Mr. Koum opposed, as did Mr. Acton, according to a person familiar with the matter.
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WhatsApp is free to users and has long eschewed advertising—the main source of Facebook’s business—leaving it with little or no revenue. But in coming months, Facebook has discussed plans to introduce ads to its “Status” feature, which allows users to post images and videos that disappear within 24 hours, much like on Instagram or Snap Inc.’s Snapchat, the person said.
Another person familiar with the matter said Mr. Koum won’t leave immediately and is expected to walk away with his Facebook stock almost fully vested. He no longer wants to work for a large company, the person added.
Facebook is expected to announce as early as Tuesday that Mr. Koum also is leaving its board of directors, that person said.
Mr. Koum didn’t respond to questions about the reason for his departure. A Facebook spokeswoman declined to answer questions. Mr. Koum is up for reelection as a Facebook director, according to Facebook’s proxy filing in April.
Mr. Koum’s departure comes as Facebook is grappling with widespread criticism about its handling of the enormous amount of personal data that it uses to fuel its lucrative advertising business. Some privacy advocates say Facebook’s targeted ad tools are incompatible with privacy. Facebook executives in an earnings call last week stressed that the company can maintain its business model while still protecting users’ privacy.
“It’s been almost a decade since Brian and I started WhatsApp, and it’s been an amazing journey with some of the best people,” Mr. Koum said in his Facebook post. “But it is time for me to move on.”
He added: “I’m taking some time off to do things I enjoy outside of technology, such as collecting rare air-cooled Porsches, working on my cars and playing ultimate Frisbee. And I’ll still be cheering WhatsApp on—just from the outside.”
Facebook Chief Executive Mark Zuckerberg, replying to Mr. Koum’s post, expressed gratitude for his work and “for everything you’ve taught me, including about encryption and its ability to take power from centralized systems and put it back in people’s hands. Those values will always be at the heart of WhatsApp.”
Privacy was WhatsApp’s hallmark, and especially important to Mr. Koum, who grew up in Soviet-era Ukraine. Messages once delivered, were removed from the company’s servers. The company once said it was built “around the goal of knowing as little about you as possible.”
The company rapidly gained global popularity, with some 450 million users by the time the founders agreed to sell to Facebook in February 2014, following five days of talks that ended on Valentine’s Day.
In August 2016, WhatsApp stirred criticism from privacy advocates when it seemed to veer from its promise by announcing it would start to share user data with Facebook.
The prospect of introducing advertising amplified tensions between Messrs. Koum and Acton and other Facebook executives, the person said. The Washington Post earlier reported Mr. Koum’s departure over the internal tensions.
In March, Mr. Acton appeared to join critics of Facebook’s handling of user data, with a message on his Twitter account saying “It is time. #deletefacebook.”
Messrs. Koum and Acton had clauses in their contracts with Facebook that allowed an acceleration of their contracts if Facebook added advertising to the app. Mr. Koum’s contract with Facebook wasn’t supposed to end until November, the person familiar with the matter said.
—Kirsten Grind contributed to this article.
Write to Deepa Seetharaman at Deepa.Seetharaman@wsj.com
Appeared in the May 1, 2018, print edition as 'WhatsApp Loses Second Founder.'