Kimbal Musk and Mr. Gracias, who left Tesla’s board last year and serves as a SpaceX director, declined to comment for this article.Today, Mr. Musk oversees or is associated with at least a dozen companies, including public ones, private ones and holding companies such as Wyoming Steel, which he uses to manage real estate. His net worth stands at about $250 billion.A Close CircleAs Mr. Musk established more companies, he collected associates he could deploy across many of the endeavors.One was Mary Beth Brown, who was hired in 2002 to essentially be Mr. Musk’s executive assistant. Known as M.B., she soon became a kind of chief of staff, handling media requests and some financial matters for SpaceX and Tesla, as well as helping to manage Mr. Musk’s personal life, said Ashlee Vance, the author of “Elon Musk: Tesla, SpaceX, and the Quest for a Fantastic Future.”That same year, Mr. Musk hired Gwynne Shotw …
