Overlord Daemon

Overlord is, self-described with no opposition or remorse, Satan. In addition to his ridiculous amount of power, his being a massive asshole also leads to most characters agreeing with this view of him.

Summary
He is the central antagonist in each of the three main Portal Daemons books, and has minor influence in Three Wishes.

Role in Portal Daemons 1
One of the biggest (and most ridiculous, at that) twists out of the many in this first book is that while in his dormant state, Overlord became truely omniscient and serves as the narrator for the first half of the book. After fully awakening, Overlord continues to narrate as he and Elyse and Eva kill Leo's friends until he leaves Tou Ergastirio for New York City.

Later, when he and Leo confront one another on top of the Empire State building, he again briefly narrates in a back-and-forth switching of perspective between himself and Leo. He is ultimately destroyed at this point when Leo pins him to the rooftop and smashes his Dark Heart.

Role in Portal Daemons 2
After Evangeleine revives him, Overlord promptly resumes his quest for universal domination, with Eva at his side.

He does not appear again for a short while, but it is made clear that he is having a merry time destroying cities and killing everything.

Eventually he and Felix also fight, with Felix employing Dynami, but this time Overlord truely dominates. Leo arrives just in time to see Over wrench Felix's Dark Heart out of his chest, crush it in his hands, and throw him down. In a fit of Rage, Leo also attacks, but Overlord tears his head off and reaches inside him to crush his Dark Heart as well. Overlord holds up Leo's head and breaks into mad laughter, asking "To be, or not to be...?" in another display of his cruel sense of humor, before laughing more and more.

Role in Three Wishes
Over has brief cameo when Sage states that "some evil is brewing back home."

He is also briefly encountered in a dream had by Roy, in his form of a snake, where he tells Roy that if he does not do anything, Sage will leave him forever and likely even die, ultimately compelling Roy to make his third wish.

Appearance
Overlord's primary ability allows him to constantly change forms. At one point in PDae2 Death comments that Overlord is constantly trying to come up with bigger and more frightening forms, which may be a slight sign of narcissm.

In Portal Daemons 1
Over's first form is a large and disproportionate man, with muscles and a heavy looking piece of armor on his torso with the emblem of the Upper Daemons emblazoned on each breastplate. His head a large and pointed metal skull with the mouth twisted into a perpertual grin that seems to grow all the larger and thus scarier throughout the book. Out of this skull his trademark large horns twist out with two smaller on top. He also of course has his great bat wings, with a wingspan of about 15' (457cm).

In Portal Daemons 2
Over is resurrected in a new form. His face is now a skull with his two large horns and two smaller horns. The teeth of the skull are pointed, and in the eye sockets there are only two small glowing red points. He is roughly 27' (823cm) tall and his wingspan has expanded to some 50' (1524cm). His body is even more disproportionate, with his extremities being long and muscular while his torso is relatively smaller and even skinny.

Disturbingly enough, he is naked.

Trivia

 * Over does not have a final form because of his constant shape shifting, although it is this that allows him to fight both Leo and Felix relatively fairly.
 * As with the above, Skotadi is probably the weakest Dark Heart weapon thus far.
 * Over is apparently an extremely easy character to write with, since his narration is basically as offensive as possible.
 * It's worth noting that only when Death is around does Overlord act reasonably personnable.
 * The very first basic design of Overlord can be traced to a demon found in the Negima series. This is nowadays most visible in his horns.