John Ternus becomes Apple's CEO on Tuesday.

He replaces Tim Cook.

Cook led the company for 15 years.

During Cook's time, Apple's value grew to $4.6 trillion.

The iPhone's popularity helped this growth.

Now Apple faces pressure in artificial intelligence.

The company has stumbled in giving promised AI features.

Earlier this year, it showed new Siri upgrades.

These upgrades focus on privacy and daily use.

Apple wants to catch up with rivals.

Ternus must go beyond his hardware engineering skills.

He needs to keep Apple strong in AI.

He also faces supply chain questions.

He must manage relations with President Donald Trump.

Trump praised Cook publicly on Tuesday.

Ternus worked on products like the Apple Watch, AirPods, and Vision Pro under Cook.

He will lead next week's iPhone launch in Cupertino, California.

Cook is expected to stay as executive chairman.

He will likely help keep Apple's ties with Trump.