Commander Hilliard was a Human male who served as a Starfleet officer during the late-24th century.
In 2375, Hilliard was assigned to Starfleet Medical on Earth. He was the supervisor for several junior officers, including Lieutenant Douglas.
That year, Doctor Julian Bashir contacted Starfleet Medical to gain information they had on the Changeling morphogenic virus, so he could cure Constable Odo. Dissatisfied with being bounced around from person to person, Bashir finally spoke to Commander Hilliard who, after asking Bashir a series of questions, denied the request as he did not have Sigma Nine Clearance.
Bashir's commanding officer, Captain Benjamin Sisko, later obtained the files for Bashir who joked that he would, "loved to have seen Hilliard's face when he realized Captain Sisko had Sigma Nine clearance." (DS9: "When It Rains...")