Ralph Johnson was a Starfleet officer in the 24th century.
In 2354, he was listed as a Starfleet Operational Support Services officer on a directory placard in Starbase 32, Maxia sector. His office was located in room #65146. (TNG: "Violations", directory)
In 2371, he was a crewmember aboard the USS Voyager. He was among the crew stranded in the Delta Quadrant, when Voyager was forcefully brought there by the Caretaker.
In 2372, as a lieutenant, he was listed on the Planetary Geosciences Division duty roster. (VOY: "Parturition")