Elon Musk just became the first person ever worth $800 billion or more after his rocket maker SpaceX acquired his artificial intelligence and social media company xAI. Forbes estimates that the deal, which values the combined company at $1.25 trillion, boosted Musk’s fortune by $84 billion, to a record $852 billion. Before the deal, Musk owned an estimated 42% stake in SpaceX worth $336 billion, based on a tender offer launched in December that valued the privately-held rocket maker at $800 billion. He also owned an estimated 49% stake in xAI worth $122 billion, based on a private fundraising round...