Jack Dorsey, CEO and co-founder of social media platform Twitter, said on Monday that he is stepping down as CEO. The 45-year-old Dorsey will remain on Twitter’s board of directors until next May, according to an email to staff that Dorsey tweeted. Twitter’s chief technology officer, Parag Agrawal, will replace Dorsey as CEO effective immediately, the company said. Agrawal began his Twitter career as an engineer, then worked his way to the C-suite, becoming CTO in 2017. As the technology chief, Agrawal has played a role in “every critical decision that helped turn this company around,” Dorsey said. Bret Taylor, a member of Twitter’s board since 2016, was also named chairman.

Dorsey said the decision to step down “was my decision and I own it,” adding in the staff email, “I decided it’s finally time for me to leave. I’m really sad…yet really happy.” Dorsey added in a press release: “I believe the company is ready to move on from its founders. My trust in Parag as Twitter’s CEO is deep. His work over the past 10 years has been transformational.”

Dorsey’s departure ends his second tenure as CEO at Twitter. He served as chief executive between 2006 and 2008, and began his second stint leading the company in 2015. Twitter, co-founded in 2006 by Dorsey, Evan Williams and Christopher “Biz” Stone, was initially a way for people to send updates to a small group using text messages. The first tweet sent by Dorsey on March 21, 2006, read “just setting up my twttr.”

Twitter has more than 5,500 employees and a market cap of about $39 billion. In the past decade, Twitter has been one of the top used social media platforms around the world, behind Facebook, Instagram and TikTok. Shares of Twitter surged Monday after Dorsey’s departure was announced. Twitter’s stock jumped more than 10% in early trading, but reversed itself by midday.

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