Amazon founder and CEO Jeff Bezos has always liked to motivate his employees by saying every day is Day 1. Well, it is actually Day 1 for his successor Andy Jassy, who officially moves into the corner office at Amazon today.

Bezos announced that he would be stepping down as CEO in February to focus on other interests including his charities Day 1 Fund and the Bezos Earth Fund, Blue Origin, the billionaire’s space company and The Washington Post, the newspaper he bought in 2013.

As he steps away, he will remain as executive chairman, but it will be Jassy, who up until now has spent most of his career at Amazon building the tremendously successful AWS cloud infrastructure arm, to keep a good thing going.

Jassy joined Amazon in 1997 and spent some time working as Bezos executive assistant and helped formulate the idea that would become Amazon Web Services, a series of integrated web services. He has been at AWS since its earliest days, helping build it from the initial idea to a $50 billion juggernaut. He was promoted to AWS CEO in 2016.

The Wall Street journal reported the other day that AWS would be ranked 69th on The Fortune 500 if it were a stand-alone company with the cloud unit currently on a $54 billion run rate. While that’s impressive he is taking over the full company, which itself ranks #2 on the same list, and which generated $386 billion in revenue last year as the pandemic pushed shopping online and Amazon was able to increase sales dramatically.

Jassy will face a number of challenges as he takes over including keeping that growth going as COVID slows down and people can begin to shop in person again. He also needs to deal with a federal government antitrust movement in the U.S. and the EU, a push to unionize Amazon warehouses and a general fear of Amazon’s growing market clout.

As part of the executive musical chairs such a shift in leadership tends to force, former Tableau CEO Adam Selipsky, who spent over a decade with Jassy helping to build the unit before moving to run Tableau in 2016, will take over as AWS CEO replacing Jassy.

In pre-market trading, Amazon stock was up 0.42% suggesting perhaps that Wall Street expects a smooth leadership transition at the company. Jassy has been a key member of the executive team for a number of years, and highly successful in his own right as he built AWS from humble beginnings to its current status, but now Amazon is his company to run and he will need to prove that he is up to the task.