More than 15 years after his very first tweet ("just setting up my twttr."), the CEO and co-founder of social media giant Twitter is stepping down, the company confirmed on Monday. "I've decided to leave Twitter because I believe the company is ready to move on from its founders," Jack Dorsey said in a statement. Twitter’s stock, which has consistently underperformed the market, jumped more than 10% at the opening bell Monday. Parag Agrawal, who has been with Twitter for more than a decade and has served has chief technology officer since 2017, will take over as Twitter CEO effective immediately, the company said. Dorsey will stay on Twitter's board until his term expires at the company's 2022 stockholders meeting.