Rosetti was a teacher at Columbia, coming home one evening to find his pregnant wife murdered– oddly in a room with all the doors and windows locked from the inside.
He takes solace in Holy Orders, joining the Priesthood from a semiconscious feeling that his wife had been possessed. During this, he is possessed himself by a demon who forces him to enucleate his right eye and burn his holy vestments.
Rosetti becomes a professional exorcist, but is constantly plagued by demons; he writes sham articles on the occult for tabloids, becoming a raging alcoholic and near-schizophrenic, tattooing holy sigils on his flesh to protect himself from his continual occult onslaught.
He eventually lifts himself out his depression during investigations with Damon Hellstrom, aka Hellstorm. Unfortunately, that relationship eventually becomes combative and Rosetti spirals back to depression and drugs.
Here he is contacted by the Asura* –“heaven’s assassins” — and given a job as a hunter of demons– even being given special weaponry specifically designed to kill demons. He eventually comes to a final confrontation with Hellstorm and is left completely psychotic. Hellstorm leaves Rosetti in the (capable) care of Isaac Christians, himself a former holy man encased in the stone body of a gargoyle.