A young programmer who saw his kidbrother play
Wolfenstein 3D and began thinking, "Fuck, I can do that too."
Thus began his lengthy oddysey of programming a 3D engine from scratch - his only inspiration was having seen Wolfenstein 3D in action.
After a long and grueling process of coding, he finally presented the first version of a game called Ken's Labyrinth. Soon after its release, the Finnish demo group Future Crew began collaborating on the game, until the game was finally released as shareware (with a real story and everything). (I think I have both versions somewhere on an old shareware release CD.)
Ken was noticed by Apogee, the company that released the original Wolfenstein, and hired him to write their new 3D game engine - now that iD software had gone into business for themselves.
The first incarnation of Ken's modified engine was seen in Rise of the Triad, which had come a significant way from Wolfenstein, and had obviously picked up a few inspirational pointers from such peers as Doom.
The second incarnation is probably the one people most readily recognize. The engine became known as BUILD, and was first presented in its full glory with the game Duke Nukem 3D, which - while not being fully 3D - competed heavily against id's Quake, which was released at the same time.
BUILD was promptly licensed to other companies, who released such half-half games as Exhumed, TekWar and various other wholly-but-not-quite-holy games.
I believe Ken's last project was working out the engine for the never-to-see-daylight project "PREY". He probably still works for 3D Realms, although they're now using the Unreal Tournament engine for Duke Nukem Forever.