Cap Fallon was an individual in a detective novel Data was reading in early 2364 to become more prepared for a Dixon Hill adventure. In the novel, he was a friend of Jim Tierney. He was, as well, the brother of Paddy Fallon and a foster father to Bud. (TNG: "The Big Goodbye")

This character was only mentioned in writing.
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 Paddy Fallon was from pages 60-61, 82, 106-107, 109, 112-113, and 130-131.