The original source is very old. Written in plain TeX. Most source files in the TUG TeX Showcase archive [1] are dated 1998. Undoubtedly the first versions were much earlier.

As the TeX Showcase master page [2] notes, the author was Steve Seiden, from LSU. He died in a bike accident in 2002.

[1] https://www.tug.org/texshowcase/cheat-20131114.tar.gz

[2] https://www.tug.org/texshowcase/