Apple CEO Tim Cook is about to take over one of the most significant parts of Apple’s business: its design team. The team currently reports to COO Jeff Williams, but once Williams begins his just-announced retirement “late in the year,” the design team “will then transition to reporting directly to Cook,” Apple says.

Having worked at Apple for nearly three decades, Williams has played a significant role in introducing the iPod and iPhone programs, leading the development of the Apple Watch, and overseeing the design team,

Apple Inc. Chief Operating Officer Jeff Williams is retiring as the company’s longtime No. 2, marking a major changing of the guard at an already tumultuous time for the iPhone maker.