Billionaire Elon Musk has brash notions for Twitter. Now, he needs to actually make them a reality. Late Thursday, Musk closed a deal to buy Twitter for $44 billion, setting the stage for massive change at the social media company. His first order of business: firing key executives at the company, including CEO Parag Agrawal. Musk's takeover of Twitter has been chaotic because he's changed his mind repeatedly about buying the social media platform. From the outside looking in, the world's richest man has been vocal about his lofty visions for Twitter's future. Now on the inside, Musk has to...