"This journey began some 27 years ago. Amazon was only an idea, and it had no name," Bezos wrote letter to employees Tuesday. "The question I was asked most frequently at that time was, 'What's the internet?' ... Today, we employ 1.3 million talented, dedicated people, serve hundreds of millions of customers and businesses, and are widely recognized as one of the most successful companies in the world."

Bezos has been Amazon's CEO since its founding in 1995. He oversaw its growth from an online bookseller into a $1.7 trillion global retail and logistics behemoth, which has also made Bezos into one of the world's richest people. Jassy has worked for Amazon since 1997 and currently serves as CEO of the company's cloud business, Amazon Web Services, its biggest profit driver.

The news came as part of Amazon's fourth-quarter earnings report.