What Jack Dorsey’s departure from Twitter means for Silicon Valley, the platform and its dedicated users. And how the new CEO, Parag Agrawal, could change the direction of the company. Read more:In a casually written tweet Monday, Twitter CEO Jack Dorsey announced that he would be stepping down from his position. As the company’s co-founder, he’s been a Silicon Valley icon for 15 years, and he leaves behind a complicated legacy. Tech reporter Will Oremus says that his departure is shrouded in mystery and that the resignation letter he posted to Twitter did not explain whether he was voluntarily leaving the company or was ousted by investors. Dorsey’s replacement is Parag Agrawal, the company’s former chief technology officer. While he’s well-liked by staff, he was an unexpected pick to head one of Silicon Valley’s most fraught and politically embroiled social media companies — and it’s up in the air whether his limited experience will limit his ability to navigate important and thorny questions around content moderation.