Commander Hilliard was a Human Starfleet officer assigned to Starfleet Medical on Earth in 2375.

That year, Doctor Julian Bashir contacted Starfleet Medical to gain information they had on the Changeling morphogenic virus, so he could cure Odo. Hilliard informed him that information Starfleet had regarding the virus was "classified under Sigma-9 clearance." When Bashir tried to contact other people at Starfleet Medical, they repeatedly transferred him to Hilliard, which Bashir was not pleased with. (DS9: "When It Rains...")