Simpson was a character in a detective novel that Data read in 2364 to familiarize himself with the Dixon Hill series. He was the servant of Russell Hastings.
Simpson was told to pay the bills and head to Montreal, where he would await a coded message from his master. (TNG: "The Big Goodbye")
The pages seen in the episode were actually from the detective novel,
The Listening Man, by author John A. Moroso. This novel was published in 1924. Information on Simpson was from page 164.