Elon Musk is running some of the world's most valuable companies. But they've been doing business with each other long before recent merger chatter around Elon Inc. The billionaire leads five major companies: Tesla, SpaceX, Boring Company, Neuralink, and xAI, which recently absorbed his social media company, X . Over the last three years, those companies have stepped up their internal dealings, buying one another's products, exchanging software and materials, and announcing investments worth