"Facebook and our products have never been more relevant to our future," Cox said in a post on Facebook announcing his return. "It's the place I know best, it's a place I've helped to build, and it's the best place for me to roll up my sleeves and dig in to help."
Cox was at Facebook for 13 years before he left in 2019. During his time at the company, Cox worked on the social network's News Feed and other key products. He led the product and design teams, and also built Facebook's first human resources teams.
During that time, Cox also butted heads with Zuckerberg over plans to integrate Facebook's messaging apps and encrypt messages from Instagram and Messenger by default. Encrypting the services could make it harder for law enforcement to fight online child sexual abuse. On the other hand, privacy advocates say encryption can protect political dissidents, domestic-violence victims and others. At theafter his departure, Cox said he and Zuckerberg "saw things a little bit differently." Cox, though, said he also left because he wanted to do something outside of social media after 13 years at the company.
After leaving Facebook, Cox became an advisor to Acronym, a progressive nonprofit. He said in his post that he spent the last year playing with his reggae band, spending time with his kids and friends, and working on climate change initiatives. At the Wired conference, Cox said Donald Trump "should not be our president" because he won't help with climate change.
"In the past month the world has grown more chaotic and unstable, which has only given me more resolve to help out," Cox said in his post. "Our most important decisions and products are ahead of us." He resumes his role at Facebook on June 22.
Cox's return to Facebook comes at a tense time for the company. Employees have criticized Zuckerberg for not fact-checking ads and posts from politicians and for leaving up posts by Trump that they say could incite violence. On Thursday, the campaign of presumptive Democratic presidential candidate Joe Biden called on Facebook tobefore it runs on the social network.
"I'm really excited Chris is coming back to Facebook!" Zuckerberg said in a post about Cox's return. A source close to Facebook said employees are pleased Cox is returning.
Cox said in his post that he was encouraged by the progress Facebook made on some of the "biggest issues facing us." Facebook has been rolling out new tools, including an online hub to direct people to more trustworthyinformation. said last week that the company is reviewing its policies, including rules around inciting violence.
Facebook has faced a string of executive departures as it's weathered a number of scandals, including over user privacy. Oculus co-founder and former CEO Brendan Iribe, Instagram co-founders Kevin Systrom and Mike Krieger, WhatsApp's Brian Acton and Jan Koum, and Oculus co-founder Palmer Luckey have all left the company. None of the other employees have returned.