Apple announced Thursday Jeff Williams, who oversaw the tech giant’s supply chain since 2010, will become its next chief operating officer.

The company made other key moves. Phil Schiller, the company’s head of global marketing, will take charge of Apple’s App Store. Johny Srouji was appointed senior vice president of hardware technologies, and Tor Myhren was named vice president of marketing communications.

The changes in leadership arrive at a critical time for Apple, as Wall Street seeks out that next hit device following the company’s launch of the iPad in 2010 and as concerns about iPhone sales growth persist.

Williams, who takes the role Tim Cook vacated when he became CEO in 2011, joined Apple in 1998 as head of worldwide procurement before managing the iPhone maker’s supply chain five years ago. Williams also played an important role in the launch of Apple’s biggest product — the iPhone — and supervises development of the Apple Watch.

“Jeff is hands-down the best operations executive I’ve ever worked with,” Cook said in a statement Thursday.

Shares of Apple (AAPL) fell 2% Thursday.

As for the change at the App Store, Schiller will “focus on strategies” to help expand its reach, the company said.

Handing App Store control to Schiller could free Eddy Cue, who oversees services including Apple Pay and iCloud, to “devote more time on TV deals,” says Creative Strategies analyst Tim Bajarin.

Apple has reportedly been working on a standalone streaming service bundling several local and cable channels accessible through its Apple TV set-top box. However, a report from Bloomberg last week claims plans were halted because media companies want more money.

Meanwhile, concerns continue to grow over sales of the iPhone. FBR Capital Markets analyst Daniel Ives says sales of the 6S and 6S Plus, launched in September, have been “lackluster” compared to previous years. In a note to investors Wednesday, RBC Capital Markets lowered estimates for Apple during the March and June quarters, slicing their price target to $140.

Shares of Apple have slid nearly 8% this month.

“Cook’s back is against the wall for the first time in a few years,” Ives says.

The management reshuffle should help Apple as it moves into new areas, such as the TV business and the often-rumored connected car market, Bajarin says.

“Tim Cook needed a solid COO and Jeff brings great knowledge of how Apple works and the discipline needed to manage all of Apple’s operations,” Bajarin says. “He is a great choice for this role.”

The reshuffling may also lead to some changes at the App Store, which includes a separate store for iOS mobile apps that run on the iPhone and iPad, and a store for apps that run on Mac computers. Although Apple’s App Store continues to flourish — it has topped 100 billion downloads — some developers have left the hub for Mac apps, complaining about delays.

And the company is bringing in some new talent to the executive suit. Myhren, former chief creative officer of ad agency Grey New York, succeeds Hiroki Asai, who is retiring.

As for Williams, Bernstein analyst Toni Sacconaghi says Williams’ appointment as COO isn’t a big surprise. “I don’t think the move will change the working dynamic between Tim and Jeff,” Sacconaghi says. “This appears to be more an acknowledgement of Jeff’s increasingly meaningful contributions to Apple.”

Follow Brett Molina on Twitter: @brettmolina23

Contributing: Ed Baig, Jessica Guynn

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