MacKenzie Bezos was not fussy, which was helpful, as there was no time for fussiness at Amazon headquarters in early 1996. She shared her office with a junior employee in a space that doubled as the company kitchen. For 12 hours a day, as workers squeezed by to use the microwave, she presided over the accounting. At night she headed to the warehouse to pack orders. She “was a huge contributor,” says Mike Hanlon, Amazon’s seventh employee. “She really is a talented person in a way that I think gets lost when you’re the billionaire’s wife.” The mystery around MacKenzie, 49, seems carefully cultivated. She largely slipped into anonymity after Amazon’s early years and has granted no interviews since January 2019, when her split from husband Jeff became public. The couple finalized their divorce in July, with MacKenzie getting 25% of his Amazon stock. That stake is currently worth $36.1 billion, enough to put her 15th on 2019’s Forbes 400. “She should have gotten 50% of the company,” says Nick Hanauer, one of Amazon’s first investors. “MacKenzie was an equal partner to Jeff in the early days.” In keeping with character, MacKenzie wouldn’t talk for this story. To shed some light on he...