Tim Cook can't run Apple forever. Who's next?

If Cook were to step down soon, these people say, he would almost assuredly be replaced by COO Jeff Williams, who emerged as the top candidate to be Cook's successor a few years ago. In 2015, Cook named Williams Apple's first COO since Cook himself held that role under Jobs. That same year, Williams shepherded the first major new product in the Cook era, the Apple Watch, to market.