Merrok was a proconsul of the Romulan Senate during the 24th century. Elim Garak claimed to have met him once, when he was working as a gardener at the Cardassian Embassy on Romulus. A few weeks later, Merrok was poisoned, one of many "unexpected" deaths within the Romulan government that year.
Years later, Odo speculated that the Romulans assassinated Merrok, and that Garak was responsible for assassinating Sub-Commander Ustard. Garak said he was "getting warmer". (DS9: "Broken Link")
This character was only mentioned in dialogue.
According to the script, the pronunciation for this Romulan's name was "mer-ROK".