The Rebel referred to a large coalition of armies which opposed the Lady and her Empire. Their leaders were a collection of wizards initially called the Circle of Eighteen. The Rebel waged war against the Imperials and their leaders, the Ten Who Were Taken, as well as the Lady's hired mercenaries, the Black Company. They besieged The Tower during the epic Battle of Charm but were defeated.
The Lady revealed that many of the Rebel leaders were working as agents of her husband, the Dominator, who was ceaselessly attempting to be freed from his centuries-old prison known as the Barrowland. In her estimation, the Rebel movement did not come about independently, but was ultimately the machination of her husband.