"Abaddon" was thought to be s a mysterious and weary traveller in search of a power source to restore him back to human form, recently he invaded Percivus and killed everyone on it, the gods then descended and trapped him within the cave, along with all the machinary. It is revealed this was all a lie in Requiem of Darkness. It is revealed he is actually the manifestation of Order in the Universe, and the rival of The Mysterious Mr. ?, the manifestation of Chaos. He is in actuallity the being that makes sure Chaos does not overwhelm the balance in the universe. He cloaks himself in darkness to hide his true identity. He is killed by ? at the beginning of Requiem, plunging not just the Fantendoverse, but all Universes into Chaos.
Being a fixed point in time and space, Abaddon has lived many different lives, his last spoken words before he was trapped in the cave on Percivus were as follows-
I am everything,
I am infinitive,
I exist in the minds of the corrupt,
And cease in the minds of the holy.