Multiple realities(covers information from several alternate timelines)
Gary Speckman was a Starfleet officer in the 24th century.
In 2353, he was listed as a Starfleet Operational Support Services officer on a directory placard at Starbase 32, Maxia sector. His office was located in room #45254. (TNG: "Violations", directory)
In 2371, he was listed as a Science Ops officer on the dedication plaque of the USS Voyager. (VOY: "Caretaker", dedication plaque) Later that year, he was among the crew stranded in the Delta Quadrant, when Voyager was forcefully brought there by the Caretaker. In that year, his name was listed on a crew manifest. (VOY: "Projections")
In an unknown, alternate future timeframe, he was listed as an Engineering Division officer on the dedication plaque of the USS Pasteur. (TNG: "All Good Things..." dedication plaque)
This character was only mentioned in writing.