During a previous extermination day, The Exorcist angels were used a Expendable muscle and as told that killing sinners would ensure the survival of Heaven's name & foundation. and so Kill by Kill, Extermination By Extermination, every angel in that past exorcism..... one angel realized that what he was doing was no better than that of Hell's crimes & evils, so he deserted his post and went to the mortal realm, wanting to know what else is out there besides humans & the life on Earth.

Throughout his travels through the stars and what he had experienced on the planets he visited, his hatred of the exorcist's crimes grew, and this Angel Deserter abandoned his old name, and Apollo was born.

One day, he came across an Exorcist squad that finally found him....and they tried to Execute him. From what we had known about Heaven's age-old history, Apollo was the first to Defy the exorcists....and survive without being killed or banished to hell as a Fallen angel

And after his defiance was revealed to the exorcist squad that hunted him down when he killed the leader of the group and before the rest were about to kill Apollo, a group of Jiralhane (Brutes) who deserted the covenant struck them down and slaughtered the exorcist executioners, inspired by Apollo's defiance against his former allies

After that, the brutes swore loyalty to Apollo and after he recruited more to join him along with the resources, weapons & vehicles they've found swathed across the galaxy, which they re-engineered and modified, The Banished was formed