An exarch was the title of an official used by the Cardassians and the Rakhari.
In 2362, Kotan Pa'Dar was exarch of a Cardassian settlement on Bajor during the Occupation. (DS9: "Cardassians")
Hadran was exarch of Rakhar's Nehelik Province in 2369. (DS9: "Vortex")
The title of exarch originates from the Byzantine Empire, and was comparable to governor.