In an illusion experienced by The Doctor, Frank was the name of Reginald Barclay's cousin.
In 2371, The Doctor experienced a series of illusions, including one in which Reginald Barclay appeared, claiming The Doctor was really Lewis Zimmerman and the crew of USS Voyager were merely holograms. Barclay claimed to be the one who programmed the holograms and that he modeled the character of Tom Paris on his cousin, Frank. (VOY: "Projections")
This character was only mentioned in dialogue.