Lord Galus is/was the fiancee of Princess Rune-Venus. Once it was revealed that he was the leader of the Phantom Tribes, that ended rather quickly.
The Phantom Tribes are a race of people who do not belong to El Hazard. In the last great war, long, long ago, the last time that the Eye of God was used, the dimensional disruption caused by the weapon pulled the ancestors of the modern-day Shadow People into El Hazard. They despise light and beauty (at least, our definition of beauty), and so hide under the ground, away from everyone else. They were the ones who kidnapped Fatora in an attempt to gain control of the Eye of God.
What they plan to do with the Eye of God is to pull their own dimension through, reducing El Hazard to the darkness of their world--the way they like things.
The Phantom Tribe members are all capable of projecting illusions that even feel like they're there. However, Nanami has the ability to see right through them.
Note: the pic of Galus here is his disguised form.