Whenever Tim Cook retires as Apple CEO, there are now several obvious contenders for the role -- but it may all come down to exactly when he steps away. Apple Park If there is one thing more certain than that current Apple Chief Operating Officer Jeff Williams will not replace Tim Cook, it's that someone from within the company will. Williams was considered a favorite until he announced his retirement, but Apple almost always promotes from within. It needs to, as well, because the pool of potential CEOs capable of running a multi-trillion-dollar company is small. The odds, too, are that any CEO appointed from outside Apple would want to change the company just to put their mark on it. Whereas many of the current Apple executives have a strong case to succeed Cook -- and partly because they have each already put their mark on the company. It's pretty certain that Apple has already chosen his successor. But until the announcement comes, it's looking like there are three candidates in the lead. Craig Federighi Easily the highest-profile Apple executive there is, Federighi also has the advantage of extensive time both inside and outside of Apple. He worked at NeXT for one thing, but he was also the chief technology officer at ecommerce firm Ariba. Craig Federighi -- image credit: Apple Within Apple, he is now senior vice president of software engineering, meaning that he is in overall charge of iOS and macOS. He's also been practically the face of Apple Intelligence, for better or worse. Craig Federighi is now 56 years old, which helps make him a prime candidate -- if Cook steps down now. Should Cook stick to his 2021 statement about probably retiring in the next ten years, Federighi might be in his sixties, and there are younger candidates. This is a situation where age has the benefit of immense experience within the company, but also shortens the amount of time it might be before the next successor is needed. John Ternus As senior vice president of hardware engineering, Ternus is Federighi's equivalent and has at least a similar track record in overseeing Apple devices. This most recently means that he's taken over Apple's robotics team, which previously reported to Apple Intelligence executive John Giannandrea. John Ternus -- image credit: Apple Ternus has overseen the introduction of AirPods, and every version of the iPad. He's also overseen the move from Intel to Apple Silicon. Plus, Ternus is 50 years old, making him the youngest of the three most likely candidates. Greg Joswiak Greg Joswiak, aged 61, has become the face of the iPhone as he has introduced the Pro models of each range for several years. He's the senior vice president of worldwide marketing, which is perhaps both a plus and a minus. Greg Joswiak -- image credit: Apple It means he hasn't had the direct, hands-on control of either software like Craig Federighi, or hardware like John Ternus. But he has arguably a broader overview of Apple than either of them, plus he has a history of working with developers to support the Mac. There are other choices These three are most likely because they are the highest-profile people in the current leadership roles at Apple. But one reason Jeff Williams was considered a favorite was that he was Chief Operating Officer (COO), and that role requires being hands-on with just about every possible element of the whole company. Williams is being replaced by Sabih Khan, 59, who does not have the same public profile yet, but has been working at Apple since 1995. Due to the nature of the COO role, it is Khan who will be expected to step in for Cook, just as Cook did for Steve Jobs. Then there is Eddy Cue, 60, who has been at the forefront of Apple Services -- an area that the company has consciously been growing for the last many years. Or there is Deirdre O'Brien, who is believed to be around 59. She's now the senior vice president of retail and people, meaning that she oversees all of the Apple Stores. She does have a bad reputation for being anti-union, but has been with Apple for over 35 years -- and is an example of why Apple promotes from within. O'Brien's predecessor was Angela Ahrendts, who was recruited from outside Apple and appears to have left the moment her initial contract was up. Apple does definitely like to promote its existing executives, and it makes a lot of sense, given the sheer scale and complexity of the company. Even if Cook were to undertake some kind of phased retirement, it's still an enormous amount for any new CEO to learn, and Apple does not have the time for any slow transition.