Satanæl

Satanæl, most commonly known simply as Satan; is a Demon, the primal race from which Devils come, and the purest of its kind. Satanæl used to be the one known as the Primordial Darkness; and was the absolute "ruler" of hell until the original Lucifer took the crown.

Appearance
Satanael is a monster of several meters of height. In the past its frame was so humongous that it could have climbed its way to Heaven if it has chosen to. Currently, it is dwarfed by Great Red, Apophis and Miðgarðsormr, but it still is a large creature.

Its body is monstrous, with proturberances sprouting out of its body, with is fleshy like bare muscles exposed without skin to cover them up. It also has bones, horns and thorns coming out of its frame. Satanael's face has no eyes, however its head has several which are perpetually open, but as he is dormant they seem to be blind.

Personality
Not much can be known about how much it retains its original self, as when it lived it was a mindless monster that followed its "chariot's" commands.

By itself, Satanael would consume and sleep, targeting anything that caught its attention, and being actively aggressive just against being threatening its rider.

History
A deity similar to the God of the Bible, who once took hell's evil miasma and turned into something entirely different for the sake of stablishing order into the world. Fully knowing that the corruption would be way too much, the deity separated itself into two beings: His body, Satanael, which would take everything and become an abomination in return; and his mind incarnated, a way less corrupted version of Satanael which would retain its real persona and who would be capable of commanding Satanael as his "rider". With the God of the Bible he became a single "coin", the two sides stablished an order and both demons and angels came to be, with right and wrong, light and darkness existing and sustaining their existences. However, ages before time, the Morning Star was expelled from Heaven and mad with rage, he decided to rule the Underworld by challenging Satanael's "mind" for the crown of Hell. Lucifer temptated the original demons; the 72 demons of Goetia allied themselves against their tyrannic master, who would not let them roma freely into the world because of his position as the keeper of Hell because of his pact with the God of the Bible.

Satanael's mind was defeated, and the fallen assimilated it, but was not compatible; unable to command the weakened Satanael, the newborn Lucifer vanished it into the depths of Hell with the incompatible power that he nonetheless held. Giving pieces of Satanael and his own power, a new race was born from the demonkind. The devils.

Plot
Maimed and with no one being capable of being its "chariot", added to the fact that the devilkind is almost, if not completely unaware of its existence, even if both angels and fallen angels were supposed to know about it, not really knowing how to tame it, and being unable to experiment on it without awakening Satanael, both factions left its existence unsaid. Thus, Satanael does not appear during canon High School DXD.

Powers & abilities
Satanael used to be as powerful (if not weaker than) as the God of the Bible himself. After its defeat at the hands of Lucifer and the rebelling demons, Satanael was left weakened and in a coma-like state. Nonetheless, it was only defeated because it lost its rider (who as a separate entity was much weaker than Satanael itself), and awakening it's an event that no one would wish for, since nowdays there are no means to meassure its strength.

As the primordial demon, he posseses the 72 pillars and extra devil's special powers.

Trivia

 * Satanael's story is heavily based on Alucard's actions in Rosario + Vampire, Satella's backstory from Re: zero and to a lesser degree Ywach from Bleach
 * His image is, of course, taken from Rosario + Vampire as well