A snapshot of the person responsible for Facebook groups and other features (but who apparently arrived too late to be in the movie…). BTW note that any WSJ.com articles I reference at this point are accessible without a subscription.
While Chief Operating Officer Sheryl Sandberg is responsible for the company's sales and relations with advertisers, Mr. Cox plays the role of chief of staff to Mr. Zuckerberg on Facebook product development—helping Facebook shape a user experience to avoid the drop-offs hitting other social networks.
Since spring, Mr. Cox and his teams have applied their theories about social design to developing the Groups feature to fix one of Facebook's biggest problems: that it doesn't always mirror real-world encounters well.
"Facebook solved this problem of getting all your friends in one place, and created the problem of having all your friends in one place," says Mr. Cox. "When something profound happens, you want all your friends to know. But when it is something that is a little more narrow, like, 'I just had a great jog.' You want to tell just some people that." He adds: "You get that mix wrong, and Facebook feels like a complete waste of time."