Bill Mensch was one of the team of eight Motorola employees and engineers who worked on the 6800 microprocessor and left the company in 1974 to work at MOS Technology along with Harry Bawcom, Wil Mathys, Rod Orgill, Ray Hirt, Mike Janes, Terry Holdt, and Chuck Peddle. He was a co-design engineer of the 6502.
In approximately March 1977, after leaving MOS Technology, Bill Mensch first worked as a microprocessor consultant at Integrated Circuit Engineering, Inc. (ICE) in Scottsdale, Arizona before founding The Western Design Center, Inc. (WDC)on May 26th, 1978 in Mesa, Arizona. Much has been written, recorded, and otherwise archived regarding Bill's work relating to the 65XX family microprocessors, and can be viewed at the Western Design Center link above and through The Mensch Foundation. A Power Point presentation regarding his history can be viewed here.
According to resume written by Bill Mensch (circa 1975/1976) found among the Holdt archives, Bill lists his duties at MOS Technology as follows:
"August 1974 - Present: Senior MOS Product Design Engineer: Microcomputer Systems Department, MOS TECHNOLOGY, INC. Valley Forge, PA. My responsibilities include Process Layout Rule Definition, Process Development (N-Channel Silicon Gate Depletion Load) support, writing MOS Device Model Computer Program, writing MOS N-Channel Design Manual. Also Co-Design Engineer of the MCS650X microprocessor family. I was responsible for the circuit design as well as the Logic Design of the Register Section and Clock Generator."