John Ternus, hardware engineering division chief, will step into the CEO role in the fall.

Apple CEO Tim Cook, speaking onstage during an announcement of new products at Apple Park in Cupertino on Sept. 9, will move into a new role as Apple's executive chair in September. Godofredo A. Vasquez - The Associated Press.

By KALLEY HUANG AND TRIPP MICKLE | THE NEW YORK TIMES

Apple's Chief Executive Tim Cook said Monday that he would step down after nearly 15 years running an operation that rode the wild popularity of the iPhone to become one of the most influential and valuable companies in the world.

Cook, 65, will move into a new role as Apple's executive chair in September and be succeeded in the company's corner office by John Ternus, the SO-year-old head of Apple's hardware engineering.

The retirement of Cook will end one of the most successful management runs in the history of U.S. business. During his tenure, Apple's annual profit quadrupled to more than $110 billion while its value ballooned more than tenfold to $4 trillion.

Cook replaced Apple co-founder Steve Jobs shortly before Jobs' death in 2011, having earned a reputation for perfecting the nuts and bolts of a global consumer electronics business. Apple has since defined how a modern technology company operates, with products assembled in a supply chain that stretches from the giant operations that Cook helped create in China to India and Brazil and a popular retail business that operates on five continents.

"He stepped into the world's biggest shoes - the biggest shoes that anybody on the planet has ever had to step into - and he's done an amazing job," said Peter Oppenheimer, Apple's chief financial officer from 2004 to 2014.

Ternus joined Apple in 2001 and rose through its ranks as he oversaw the development of Macs and iPads. He will be Apple's eighth CEO since its founding 50 years ago and its third since Jobs returned in 1997 to pull the company from the brink of bankruptcy.

"I am filled with optimism about what we can achieve in the years to come," Ternus said in a written statement. "I promise to lead with the values and vision that have come to define this special place for half a century."

Ternus will take over a company that has not created a new mainstream product in a number of years and faces questions about its business.

Apple has lost several top executives in recent months, worrying investors about the depth of its next generation of managers and its long-term strategy, particularly with artificial intelligence. The company has largely stayed on the sidelines as the rest of the technology industry has committed to spending hundreds of billions of dollars developing AI.

Apple is also navigating increasingly choppy political waters, including whiplash over the Trump administration's tariffs, a looming antitrust trial and geopolitical tensions with China.

In recent years, Cook, out of necessity, had become the technology industry's leading diplomat, making regular visits to Washington and Beijing to try to manage the often conflicting agendas of President Donald Trump and Xi Jinping, China's leader.

Even so, Apple is still one of the most profitable companies in the world, thanks to the stability of sales of its iPhones, other products including the Apple Watch, and services including iCloud andApple Pay.

Ternus' hardware engineering division will be taken over by longtime deputy Tom Marieb, according to Bloomberg. He will report to newly named Chief Hardware Officer Johny Srouji. In that role, Srouji is gaining oversight of a newly combined hardware engineering and hardware technologies group.