Apple’s John Tarnas will be running one of the world’s most powerful companies. That job is a minefield

Through his 15-year reign as Apple’s top banana, Tim Cook became instantly recognizable, powerful beyond imagination, and extremely wealthy. Most estimates put Mr. Cook’s current net worth at about $3 billion, a fortune he accumulated primarily through performance-based stock compensation as Apple’s market capitalization grew more than 11 times under his watch, to about $4 trillion.

But this job also comes with a lot of baggage. Mr. Cook also had to navigate two Trump administrations and one Biden administration, each with its own stance on Big Tech, China, and regulation. Mr. Cook also faced off with the FBI over encryption, spent years defending the App Store in court against accusations that Apple had turned the iPhone into an illegal monopoly, and made compromises to stay in the Chinese market that drew unwanted attention from human rights groups. Cook last saw the Vision Pro headset, the company’s most ambitious hardware bet, win over consumers. This says nothing about AI, and the results are still unknown. Incoming CEO John Tarnas will take over all of that.

Here are some of Cook’s biggest battles over the years.

Do we all remember the FBI encryption battle in 2016? After a mass shooting at a holiday gathering in San Bernardino, California, the FBI demanded that Apple help unlock the shooter’s iPhone. Cook rejected this, arguing that encryption was the only meaningful protection against the exposure of people’s personal data, and that being forced to break it would set a dangerous precedent. The standoff ultimately ended with the FBI finding another way into the breach, but it cemented Apple’s identity as a privacy company and forged long-standing tensions with governments around the world. Ternus inherits that identity and the obligations that come with it.

For Cook, the App Store antitrust battle was no mean feat. Epic Games sued Apple in federal court over the requirement that apps use Apple’s in-app payment system and a 30% cut of sales (and when the judge pressed Cook on why users couldn’t simply pay developers directly for a lower price, Cook’s answers did little to quell her skepticism). In 2021, Apple almost won the case, with the court refusing to call it a monopoly but ordering it to allow developers to link to external payment options. The company complied in the narrowest sense, charging a 27% fee (some discount!) on outside purchases, but the court found this in contempt. The Ninth Circuit Court of Appeals upheld the ruling in late 2025, and after a request for reconsideration was denied last month, Apple is now preparing to appeal to the Supreme Court, which had already refused to hear the earlier suit. Lower courts will have to decide what fees Apple can actually charge.

This epic saga is just one front in a broader antitrust war. In March 2024, the U.S. Department of Justice charged Apple with illegally dominating the smartphone market by restricting third-party app and device developers, including competing smartwatches, digital wallets, and messaging services, in ways that make it difficult for users to switch from iPhones. A federal judge denied Apple’s motion to dismiss the case, meaning the case could be fought in court for years. And just this week, Apple revealed it faces a potential $38 billion fine in India, where regulators found the company guilty of abusing its dominant position in the app market and refused to provide required financial data. The case is complicated by the fact that Apple’s market share in India is still relatively low at about 9%, making it an unusual angle to challenge the findings. Ternus has taken over this battle midway through, and the App Store’s revenue model is under direct judicial threat.

China is also always engaged in an increasingly uncomfortable balancing act. Mr. Cook built Apple’s manufacturing operations around China’s supply chain, leaving the company deeply dependent on a country that has become increasingly assertive and unpredictable over time. He also made some unpleasant concessions regarding business operations in the Chinese market. Most notably, it removed VPN apps from China’s App Store and stored Chinese users’ iCloud data on state-controlled servers. Cook proved adept at shielding Apple from tariffs and trade war risks during President Trump’s first term. Part of that was fostering a personal relationship with Trump. Trump responded to the news of Cook’s retirement, calling him “a great guy!” Apple has already indicated that Cook, as chairman, will continue to help Ternas negotiate the geopolitical terrain. This is an acknowledgment that these relationships are difficult and that Mr. Cook’s institutional knowledge remains extremely valuable.

But AI is perhaps the most pressing unresolved challenge facing Ternus. John Gianandrea, Apple’s head of AI, will officially leave the company this month after repeated delays in rolling out Siri, which uses more sophisticated AI. Rather than relying solely on its own model, Apple turned to both Google’s Gemini and OpenAI’s ChatGPT to power some Apple Intelligence features. Bob O’Donnell, a longtime market research analyst, told Reuters on Monday that Ternus’ biggest challenge will be “bringing together a better AI story and product that relies on Apple’s own capabilities rather than third parties,” but some argue that the company will look wise in hindsight given the high-stakes competition among today’s biggest AI companies.

Last but not least, Apple’s executive changes are less discussed, but they do make sense. Ternus takes over a significantly restructured management team after several other Apple executives, including longtime COO, general counsel and head of UI design, have departed over the past year. This is both a challenge and an opportunity for him to make his own assessment of things relatively quickly.

What ties most of these challenges together is that Mr. Cook’s greatest skill was his ability to manage complex relationships with governments and partners while keeping the business on track. One of the more interesting questions in the transition may be whether Mr. Turnus has the same skills or whether Mr. Cook will remain as executive chairman to fill a void.

The scarier question at stake in Ternas’ tenure is whether the world that made Apple the most valuable company on earth could actually end. Many industry watchers believe that AI agents will become the primary way people interact with services, and the App Store and its 30% cut will become a distant memory. Combine this with the prospect of exciting new hardware, like OpenAI currently in development, eroding the iPhone’s grip on our lives, and Tarnas may be on his way to navigating more than complicated relationships and lawsuits.