Multiple realities(covers information from several alternate timelines)
Keith Rockefeller was a Starfleet officer in the 24th century. His serial number was KI-379-0021 MND.
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 an alternate timeline, his name was listed on the crew manifest read by Harry Kim in early 2372. (VOY: "Non Sequitur")
In 2376, his name was listed on a crew manifest. (VOY: "11:59")