Elon Musk, who runs four other companies, will now be Twitter CEO

Tesla Inc boss Elon Musk said in a filing on Monday he will serve as chief executive of Twitter, the social media company he just bought for $44 billion, a move that Wall Street analysts have said could stretch the billionaire thin.

Musk, who also runs rocket company SpaceX, brain-chip startup Neuralink and tunneling firm the Boring Company, fired Twitter’s previous chief, Parag Agrawal, and other top company officials last week.