The GuiMon in Chief was a title held by a Ferengi military officer who was in command of the Ferengi Alliance fleet. It is equivalent to the rank of Admiral in Starfleet.
As with any position of command within the Ferengi Alliance, including the Grand Nagus, the GuiMon in Chief was able to demand a sizable percentage from any profits that were made by a DaiMon in the fleet. (TNG novel: The Buried Age)