Ophelia the Fallen Angel 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".
Ophelia tends to be the "brains" behind any operation Valvoga does and tends to be rather subtle in her manipulations. Whenever someone else tries to manipulate or pressure Micky, Ophelia steps in though she is primarily doing it out of self-interest as no one controls Valvolga but those who are part of Valvolga. At the end of the game she is revealed to be the mysterious force in the game known as "The One".
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.