R. Scott Campbell is one of the masterminds behind the original Fallout and its original lead designer. Among other contributions, he wrote the story for the game and laid out many of the major non-player characters and locations.
Campbell left Interplay when the game was still in development, after which Chris Taylor took over as lead designer. In 2012, he wrote a lengthy article entitled The Origins of Fallout and submitted it to No Mutants Allowed, detailing the creative process involved in bringing the first Fallout game to life.
I'm not going to go anywhere near the argument of who is responsible for Fallout's greatness, except to say that Scott Campbell never gets the credit he deserves in all these arguments. He wrote a lot of the original story and came up with a lot of the characters and places as well.