Probably like half of the big ones you've heard of were initially created by one person. Python was Guido Van Rossum, PHP was Rasmus Lerndorf, C++ was Bjarne Stroustrup, D was Walther Bright.
If that list included hobby/proof of concept languages like the one Terry created, almost all of them would be created by one person.
Terry Davis is dearly missed, and was clearly a skilled programmer, but he wasn't some once-in-a-generation genius that was cursed with madness. He's not John Nash or anything. Just a clever schizo who made some interesting stuff, and more importantly said some absolutely histerical shit.