What happened

On Thursday, Twitter (NYSE:TWTR) stock fell almost 4% following a Nov. 9 announcement that the company's chief operating officer, Adam Bain, was leaving "to explore new opportunities." While the stock is up slightly on Friday at the time of this writing, shares are still trading about 3% below the stock's price earlier this week, before Twitter issued a press release about the executive's departure.

Twitter headquarters. Image source: Aaron Durand (@everydaydude) for Twitter.

CFO Anthony Noto will replace Bain and simultaneously step down from his CFO role, though Noto "will continue as the CFO until a new CFO is appointed," Twitter said.

According to Twitter, "As COO he will continue to manage the live content business, and assume responsibility for Twitter's revenue generating organizations including global advertising sales, data, revenue product, and MoPub, as well as global partnerships and business development, effective immediately."

Bain will stay to "assist with the transition of the COO role over the coming weeks."

Does it matter?

Bain's departure represents an important loss for Twitter. As CEO Jack Dorsey acknowledged in the press release, Bain built "a global business from the ground up." In other words, Bain essentially built Twitter's advertising business.

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