Clark was an assembly language programmer who worked as a “Saturday afternoon ‘handyman’ programmer” at Exatron, on their stringy floppy system. He worked on interfaces to Digital Group and Timex/Sinclair 1000 computers.
He wrote a series of program he called Source Code Generators that would produce commented source code from CP/M in memory. One of his disassemblies became the basis for modern re-implementations of CP/M.
He also wrote a version of CP/M for the Timex/Sinclair 1000, which he called ZCPM, as it was optimized for the Z-80. It was burned into an EPROM and sat in the 8-16k memory space. The source code for ZCPM is available on archive.org.