Incoming CEO John Ternus spent years building the credentials that could put him at the helm of Apple: engineering expertise, a record of delivering major products, relationships across the company, and the trust of its top leadership.

Now comes the bigger test: Can he lead one of the world’s most successful companies into its next era of innovation?

In a new Fortune feature, my colleague Sebastian Herrera examines the challenge awaiting Ternus as he prepares to succeed Tim Cook. Cook transformed Apple into an operational powerhouse.

Annual revenue has grown by more than $300 billion since he became CEO in 2011, profits have more than quadrupled, and Apple now has 2.5 billion active devices around the world.

Yet former employees, investors, and analysts say Apple has struggled to produce the kind of category-defining products that marked the Steve Jobs era, as design lost influence and product launches increasingly focused on refining existing hits.