Jim Keller, who has been behind some of the biggest CPU core design projects with AMD and Apple has walked away from designing AMD’s Zen CPU.

The move should be a blow as we think AMD needs all the help it can get at the moment, and Zen is either going to save the company or be its swan song.

Samsung will use Keller to design newer, bigger chips, or perhaps even smaller, low-power chips, as the company gears up for the internet of things.

Keller’s CV is impressive. He worked at DEC until 1998 and helped design the Alpha 21164 and 21264 processors. In 1998 he moved to AMD, where he worked on the Athlon (K7) processor. He was the lead architect of the AMD K8 microarchitecture and designed the x86-64 instruction set and HyperTransport interconnect.

In 1999, he worked at SiByte which was bought by Broadcom. He was chief architect until 2004 when he moved to P.A. Semi. At the time PA Semi was making low-power mobile processors and it was bought by Apple in 2008. As part of Jobs’ Mob Keller was part of the team to design the Apple A4 and A5 system-on-a-chip mobile processors which ended up in the iPhone 4, 4S, iPad and iPad 2.

In Keller returned to AMD to work on Zen. It is not clear why he is going, just before the Zen chip gets its act together.