CNET:

Gerard Williams III, senior director in platform architecture, departed Apple last month after nine years, according to a person familiar with the matter.

While not well known outside of Apple, Williams led development of every Apple processor core from the A7 — the first 64-bit processor for mobile devices — to the A12X, the chip powering Apple’s latest iPad Pro devices.

And:

Williams isn’t the first notable Apple engineer to leave its chip business, which is led by Johny Srouji. Two years ago, Apple SoC architect Manu Gulati left for a similar role at Google. After Gulati left Apple, Williams took over his role overseeing SoC architecture.

Hard to know how much of an impact Williams leaving will be. Feels like Apple’s chip design process is mature enough that no one is irreplaceable.