The Rucker empire is mentioned by the people of Providence as being a nation of cruel barbarians. They believe that the Rucker army will eventually attack them and steal their Goddess Statue, but it is revealed that the army are actually monsters on orders from the Demon Lord. Rucker was once the main power on their island thanks to their military prowess and swordsmanship, as opposed to the wizards of Hubble. However, that changed after an attack on Hubble, which resulted in the death of Lucia, a childhood friend of Prince Hybris. Hubble was forced to become a vassal nation to the Ruckers after the raid, but Prince Hybris swore to become powerful enough to destroy the Ruckers.
Rucker is now a shadow of its former glory. The castle is in shambles and the people are forced to build after the wizards of Hubble have attacked. Even though the Ruckers aren't considered a rival power to Hubble anymore, King Hybris is still paranoid that they could still rise up and attack them again someday.
The Rucker Empire has ceased to exist in the present, likely owing to the fact that Hubble practically decimated them.