(CNN) — Elon Musk on Friday named longtime media executive Linda Yaccarino as the new CEO of Twitter, months after he promised to step back from the role.

“I am excited to welcome Linda Yaccarino as the new CEO of Twitter!” Musk wrote in a tweet on Friday. He said she “will focus primarily on business operations, while I focus on product design & new technology.”

Earlier in the day, Yaccarino announced that she was leaving her role as chairman of global advertising and partnerships at NBCUniversal.

“It has been an absolute honor to be part of Comcast NBCUniversal and lead the most incredible team,” she said in a statement Friday. “We’ve transformed our company and the entire industry.”

As CEO, Yaccarino will face a long list of challenges that have piled up under Musk’s ownership, including an advertiser exodus, service disruptions, regulatory scrutiny and a growing list of rivals. Musk’s controversial policy changes and statements have also alienated some longtime Twitter users.

Even as Musk steps back from the CEO role, he will likely still maintain significant control over the future direction of the company. Musk previously said he would serve as the company’s executive chairman and CTO, as well as being the owner of the platform.

A seasoned media executive

Musk has clashed with mainstream media outlets and also said he hates advertising. But Yaccarino represents both those worlds.

Yaccarino has been at NBCUniversal for more than 11 years, returning to the company where she started as a college intern. Before that she was executive vice president/COO of advertising sales, marketing and acquisitions at Turner Broadcasting, which included CNN at that time.

At NBCUniversal, she oversees a 2,000-member global team, according to her company profile. That would be more people on her team than are left working at Twitter, which Musk said in an interview with the BBC last month is down to 1,500 people after multiple layoffs under his watch.

NBCUniversal’s ad sales team has generated $100 billion in ad sales since she joined in 2011, according to her profile, and forged partnerships with many new media companies including Twitter as well as Apple News, Buzzfeed, Snapchat and YouTube.

Last month she appeared with Musk at an industry conference for a session entitled “Twitter 2.0: From Conversations to Partnerships.”

Yaccarino’s most notable achievement at NBCUniversal is creating unified ad sales teams rather than having 15 different sales teams approach the same advertisers.

“We were difficult to do business with,” she said in an interview with Salesforce describing the consolidation.

The loss of Yaccarino comes at a bad time for NBCUniversal. Ad revenues are down throughout the media industry, prompting cost cutting and in some cases layoffs across many companies. NBCUniversal has had some job cuts of its own, although not as deep as those at some of its rivals.

Media companies, including NBC, are scheduled to make “upfront” presentations to advertisers next week in an effort to win ad commitments for later this year. NBC’s session is set for Monday morning.

Yaccarino would not be the first or only woman running one of Musk’s companies.

Musk previously tapped, Gwynne Shotwell, to run SpaceX. She is president and COO of the company, while he holds the CEO title. But she’s credited by some in the industry as a key to SpaceX becoming the world’s most successful commercial rocket company.

Robyn Denholm also serves as chairman of Tesla. She assumed that role from Musk when the SEC required him to give up the position after a tweet in which he claimed he had funding secured to take the company private, when he had not yet locked up the financing to do so.

Denholm has kept a low profile at Tesla, not speaking at an investor day earlier this year at which 15 other Tesla executives in addition to Musk spoke

Twitter’s advertiser exodus

The choice of Yaccarino may hint at Musk recognizing the limitations of his efforts to make Twitter less dependent on advertising.

Ad sales represented more than 90% of the company’s revenue before Musk purchased it in October. But many advertisers have fled the site since then.

Earlier this year digital marketing analysis firm Pathmatics by Sensor Tower reported that 625 of the top 1,000 Twitter advertisers, including major brands such as Coca-Cola, Unilever, Jeep, Wells Fargo and Merck, had pulled their ad dollars, based data through January 25. Monthly revenue from those previous top 1,000 advertisers plummeted by more than 60% from October through January 25, from around $127 million to just over $48 million, according to the data.

Many advertisers have been concerned with Musk’s severe staff cuts, the apparent rise of hate speech, and controversial policy decisions, including his move to invite users back to Twitter who had previously been banned.

General Motors said it would pause paying for advertising on Twitter while it evaluates the platform’s “new direction.” Musk blamed the exodus on “activist groups pressuring advertisers, even though nothing has changed with content moderation.”

Musk has tried to increase revenue by racing to bolster its subscription business, charging for the blue checkmarks that verify a user’s identity, with limited success. As a result, he may have little choice but to revive Twitter’s relationships with advertisers and boost its core advertising business.

Musk has previously spoken about improving ad sales by focusing more on the relevance of its ads.

Pressure to find a new Twitter CEO

Ever since he first expressed interest in buying Twitter, the share price of Tesla has suffered. Investors have been worried that his fascination with Twitter was distracting him from the challenges facing the electric automaker.

Musk announced the CEO news shortly ahead of Tesla’s annual shareholder meeting, which is set for Tuesday.

Shares of Tesla closed Thursday down 55% from where they were 13 months ago when his initial purchase of a 9% stake in Twitter was disclosed. Shares of Tesla were up 3% in early trading Friday just after the open, before losing most of that gain.

“We believe Musk leaving CEO of Twitter earlier than originally thought … is a positive development for Tesla as well as SpaceX with Musk needing to spend more and more time on these golden child platforms rather than Twitter,” wrote Dan Ives, analyst with Wedbush, in a note to clients Friday.

It may also be welcome news for Twitter users. Musk promised he would find a new CEO to run Twitter last fall after 57% of those who participated in a Twitter poll he posted voted that he should give up the job. In December he vowed to name a replacement “as soon as I find someone foolish enough to take the job!”

Elon Musk names NBCU ad chief Linda Yaccarino as Twitter CEO