Luca is the young son of Father Sullivan, murdered by Valentine Volmari by biting into his throat. His full name was D’arby Luca Sullivan Jr, sometimes called just Dar by his friends.
He has been unbeknownst to everyone else, turned into a form of Dhampir by Valentine. Retaining his mostly childish worldview, his body turned into an ever-growing, ever-taller corpse as a result of his transformation.
Due to his throat being ripped out, he is mostly mute, requiring support to have semblance of speech, done by stuffing fingers into his open neck and down his throat.
He attempted to create more dhampirs like him, but was unable to, only created more mindless monsters to his horde. This failure to do so made him hold a bit of a grudge against Valentine, wanting to be like him.