Interestingly, there's a lot of debate about this. BGG lists him as both Michael E and Michael S (or rather, associates games with Michael S printed on them with Michael E). I'm sure you've probably discovered this in your search.
Apparently Matheny is also a popular name, though I had never heard of it. I think calling each Michael S and Michael E to try to get verification would take awhile.
Here's the profile for MEM: https://boardgamegeek.com/boardgamedesi ... -e-matheny
You've come across a great mystery here and I haven't solved one of those since the Leonard Patt fireball.
I'll see if I can come up with anything concrete.