Apple has named its head of hardware engineering, John Ternus, as its new chief executive officer to replace Tim Cook, marking a major leadership transition at the world’s most valuable tech company.

Cook, 65, will step down from the CEO role on September 1 after a 15-year tenure that transformed Apple into a $4 trillion company and cemented its dominance in the global smartphone market. He will remain with the company as executive chairman.

Ternus, 50, has spent more than two decades at Apple and currently oversees engineering for key products including the iPhone, iPad and Mac. He is widely seen as a long-term internal successor and has played a central role in hardware development in recent years.

Apple said outgoing chairman Arthur Levinson will step down from his role as non-executive chairman but will remain on the company’s board of directors.

In a statement, Cook called his time as CEO “the greatest privilege” of his life, adding that he was grateful to work with “ingenious, innovative, creative, and deeply caring people.”

Ternus said he was “profoundly grateful” for the opportunity to lead Apple forward and continue its mission.

Cook took over as CEO in 2011 after the death of co-founder Steve Jobs, and oversaw an era of massive expansion driven largely by the iPhone. Under his leadership, Apple became the first publicly traded company to reach a $1 trillion, $2 trillion and $3 trillion valuation, and is currently valued at about $4 trillion.

However, Apple has faced growing pressure in recent years due to slower progress in artificial intelligence compared with rivals such as Nvidia, and its reliance on external partnerships to enhance products like Siri.

The leadership transition comes at a critical moment as artificial intelligence reshapes the global tech industry.