Dryzen the Star Dragon is one part of a an overlord collectivly known as Dark Lord Valvoga. Micky forms the upper body, Dryzen forms the lower body in the form of a gigantic dragon skull with a glowing red orb within its mouth, and Ophelia forms herself into a head in a hole in Dryzen's skull, placing herself directly in the center of the "body".
Dryzen bullies Micky around purely for fun as well as when there is the possibility for it to benefit himself. Dryzen is massive, insane, and his most common statement is little more than "Kill!".
Valvoga as a whole serves as the image for the Tera Star Spell in Disgaea 2.
Source: Wikipedia, "Makai Kingdom: Chronicles of the Sacred Tome," available under the CC-BY-SA License.