J. Billingsley was a Human Starfleet medical officer in the 22nd century.
In January of 2155, he was named as a Flight Surgeon on one of the directory placards at Fleet Operations Center, Sol Sector. He shared an office in room #5555 with "Space Hero" S. Bakula, science officer J. Blalock, tactical officer D. Keating, "Top Gun" A. Montgomery, communications officer L. Park and engineer C. Trinneer. (ENT: "Demons", directories)
The name was an in-joke reference to Star Trek: Enterprise star John Billingsley, who played Phlox, the chief medical officer aboard the Enterprise NX-01.