Sub-commander Ustard was an officer in the Romulan military.
He was killed in a transporter "accident" the same year that Elim Garak worked as a gardener at the Cardassian embassy on Romulus. Circumstances suggested that Garak was responsible, though no proof ever emerged. (DS9: "Broken Link")
This character was only mentioned in dialogue.
According to the script, the pronunciation for this Romulan's name was " 00-stard".