Jack Dorsey stepped down Monday as CEO of Twitter, the social media site he co-founded in 2006 and navigated through the tumultuous years of the Trump administration and increasing calls for regulation from lawmakers around the world.

He was replaced by Parag Agrawal, who as the company’s chief technology officer had recently been working on technologies associated with cryptocurrencies, which have become a fascination of the tech industry’s power brokers, including Dorsey.

Dorsey’s exit marks a significant shift at the company, which has navigated years of pressure from investors who thought it did not make enough money and criticism from Washington, particularly from Republican lawmakers who have complained Twitter has helped stifle conservative voices in social media.