Apple's new CEO John Ternus takes over from Tim Cook at a pivotal time

John Ternus is taking charge of Apple at a moment when the company's long-running hardware strengths face a disruptive challenge from artificial intelligence.

His appointment on Tuesday ends Tim Cook's 15-year tenure as chief executive. During Cook's leadership, Apple's value climbed to $4.6 trillion, driven by the enormous popularity of the iPhone. Cook is expected to remain influential as executive chairman.

Ternus, a hardware engineer who worked on major Apple products including the Apple Watch, AirPods and Apple Vision Pro, now has to move beyond his traditional area of expertise. Apple has struggled to deliver new artificial-intelligence features promised nearly two years ago, while rivals have advanced in the technology. The company unveiled new AI capabilities earlier this year, including upgrades to Siri, and emphasized privacy and everyday use as it tries to catch up.

The new chief executive will also have to navigate Apple's supply-chain questions and its relationship with President Donald Trump. Cook built ties with Trump while guiding the company through business challenges, including the president's trade and tariff campaign targeting Asian countries where Apple relies heavily on manufacturing. Trump publicly praised Cook on Tuesday, and Cook is widely expected to help preserve that relationship after moving into his new role.

Ternus will appear prominently at next week's launch of the latest iPhone at Apple's headquarters in Cupertino, California. The event will offer an early public test of the new era beginning under his leadership.