Jeff Bezos has a formulation about one-way doors and two-way doors — decisions that are irreversible and permanent and those that can always be unwound. Stepping through what is almost certainly a one-way door last week, Bezos said he will resign as chief executive officer of Amazon.com Inc. and become executive chairman later this year.

Bezos will hand day-to-day control to Andy Jassy, his longtime head of Amazon Web Services, a swiftly growing division that has almost single-handedly changed the way companies buy the technology that powers their businesses.

With that comes at least a partial end to one of the most epic runs in modern business history. Yet, the move feels, in many ways, natural and even inevitable. Over the last 25 years, the Amazon founder led the company through perhaps the most fertile period of any American business ever. Amazon was first just an idea at the Wall Street hedge fund D. E. Shaw & Co., where Bezos was a vice president; then it was an online bookseller and high-flying dot-com stock during the late 1990s.