Admiral Chapman was a 24th century Starfleet flag officer.
In 2374, while attempting to decode the jumbled data transmission from Earth, Kathryn Janeway joked that the data clusters could simply be Chapman's recipe for the perfect pound cake. (VOY: "Hope and Fear")
It is unclear if Admiral Chapman is the same individual as Professor Chapman, both of whom are individuals known by the members of USS Voyager's crew.