D. Koeppel was a Human Starfleet officer in the 22nd century.
In 2154, he was listed as a Flight Software officer on the dedication plaque of the Columbia NX-02. (ENT: "Affliction", dedication plaque)
In January of 2155, he was listed as a Robotic Systems officer at Starfleet Command's Fleet Operations Center, Sol Sector. His office was located in room #4233. (ENT: "Demons", directories)
This character was only mentioned in writing.