Apple has named John Ternus as its new chief executive to replace Tim Cook who is stepping down after 15 years of leading the technology giant.

Ternus, currently the head of hardware engineering who has been at Apple for 25 years, will take over on 1 September and Cook will become executive chairman.

Cook has been chief executive of Apple since 2011 after co-founder Steve Jobs resigned for health reasons, shortly before his death.

Cook will stay as chief executive through the summer to work with Ternus on the transition after which he will "assist with certain aspects of the company, including engaging with policymakers around the world".

Cook's decision to step away from the chief executive role follows months of speculation that Apple was looking for a successor.

He described the job as "the greatest privilege of my life" and during his tenure he led the company to become one of the most valuable in the world.

In 2018, Apple became the first public company to be valued at $1 trillion (£740bn). It is now worth $4 trillion.

Cook described Ternus as a "visionary" executive with "the mind of an engineer, the soul of an innovator and the heart to lead with integrity and honour".

"He is without question the right person to lead Apple into the future," Cook added.

Ternus emerged as a favourite to replace Cook last year, after another long-time executive, chief operating officer Jeff Williams, left the company.

During his quarter century at Apple, Ternus has worked on essentially every major product the company has released, including every generation of the iPad, many generations of the iPhone, and the launch of AirPods and the Apple Watch.

He also oversaw the transition of Mac computer processors to Apple's own silicon.

Ternus also worked under Jobs. In a statement on Monday, he referred to Cook as his "mentor."

"I am filled with optimism about what we can achieve in the years to come," Ternus said.

Naming a leader who comes from a product and hardware background may allow Apple to emerge from a constant criticism of Cook's tenure, that it was no longer innovative enough.

While Cook oversaw a four-fold increase in Apple's yearly profit, with a massive expansion in products sold around the globe, its product line has remained largely static.

Dipanjan Chatterjee, a principal analyst at Forrester, praised the financial stability Cook brought to Apple, but noted he had not given the company a product like the iPhone which would give Ternus another 20 years of success.

He said Apple "remains structurally dependent on the phone" as it "searches for its next growth engine".

The appointment of Ternus shows Apple is looking for "differentiation" in its products, said Chatterjee, adding that the new leader "must resist the temptation of incrementalism that has plagued Apple of late and escape the iPhone's gravitational pull".

Ken Segall, who was Steve Jobs' creative director for more than a decade, told the BBC: "I don't think Tim ever really shook the operations guy vibe.

"I think when people talk about the difference between Steve and Tim, that was basically it – Steve the visionary, Tim the operations guy who took over."

Gil Luria, managing director at DA Davidson & Co, said having someone so hardware-focused at the helm now shows Apple is going to put more energy into new products, like foldable phones and wearable devices like eye glasses.

The tech giant has also faced criticism for being slow to jump on the soaring demand for artificial intelligence (AI), and has ended up integrating OpenAI's ChatGPT technology in its operating systems.

Following Monday's announcement, OpenAI's Sam Altman wrote on X: "Tim Cook is a legend.

"I am very thankful for everything he has done and I am very thankful for Apple."

Cook did not come from a hardware or product background when he joined Apple.

Instead, he had spent many years as a business operator at companies like IBM and Compaq. He was a tech executive focused on operations and fulfillment, logistics and sales figures, less so thinking up and launching new technological products.

That was what Jobs was best-known and lauded for.

One of the most significant product launches during Cook's leadership was the Apple Vision Pro, a virtual and augmented reality headset that did not catch on with buyers.

Nevertheless, his skill as an operational executive will see him widely remembered as one of the most successful business leaders.

Timothy Hubbard, a professor at the University of Notre Dame Mendoza College of Business, said Cook's era of Apple turned it into a company that was "the best at refining, scaling and defending an extraordinarily powerful system".

"The real question now is whether that same organisation can pivot toward exploration, where success depends on speed, uncertainty and a greater willingness to experiment," he said.

Apple's apparent reluctance to dive head first into AI products and services has set it apart from others like Google, Microsoft, and Meta, which are spending hundreds of billions of dollars a year to get ahead in this area.

With a new boss, Apple may be showing its strategic interest in deeper integration of AI into its hardware, said Hubbard.

"The very strengths that made Apple dominant - their discipline, polish, and control - could become constraints if the next era rewards openness and faster iteration," he said.

"That rapid innovation is where Apple started, and maybe that's where the company needs to return."