It took some experimentation—including a strange attempt to move with WADX—but Fong settled on WASD and has been using it since Doom. Did he invent the scheme? No, probably not. Others were also gravitating to the left side of the keyboard for Doom at the same time. But without Fong's influence, the default could have ended up different. It might have been EDSF, or stranger configurations like ZXC to strafe and move backwards, and the right mouse button to move forwards. Some early shooters bound movement to the arrow keys. In 1994, System Shock used ASDX, while Descent used AZ for forward/reverse and QE for banking (if you didn't happen to have a joystick).
Fong tells us he even knew a player who used ZXCV to move.
“I’m certainly not going to take credit for the creation of [WASD],” says Fong. “I stumbled across it. I’m sure other people started using it as well just based on what was comfortable for them. I definitely think I helped popularize it with a certain set of gamers, particularly the ones that played first person shooters.