Chief Archon, or simply Archon, was a Cardassian title, roughly equivalent to that of a magistrate. The Chief Archon presides over the Supreme Tribunal, and was addressed as "Madam Archon".
Makbar was the Chief Archon on Cardassia Prime in 2370. She presided over the trial of Miles O'Brien, who was charged with smuggling weapons for the Maquis. (DS9: "Tribunal")