Robert Smith is a character mentioned in Fallout 4.
Robert "Bobby" Smith was a boy who lived before the Great War. He was admitted into the Parsons State Insane Asylum on August 10, 2074, at the age of 9 going by his birthdate of November 23rd, 2064. The patient notes state his constant laughter is ceased only by Johann Sebastian Bach's Toccata and Fugue in D Minor. 
Toccata and Fugue in D Minor, despite being a classical piece, does not actually play anywhere in-game.
Robert Smith is mentioned only in Fallout 4.