Owen is the Antichrist.Notice that everyone seems to love him, despite being shrewd and obnoxious. Furthermore, despite all his messianic asperations, everyone he influences is left depressed and emotionally stunted, and in the case of Johnny's mother, dead. Furtherfurthermore, his death was a Senseless Sacrifice. The assailant that he was protecting the Vietnamese children from was only there because Owen had provoked him in the first place.
Rev. Merrill is Owen's biological father.Owen's parents claim that he was immaculately conceived. In reality, Merrill's miserable family life led him to sleep with Mrs. Meany around the same time that he had his affair with Tabitha. Since the elder Meanys are superstitious and somewhat naive, it's possible that they don't understand how reproduction works (e.g. thinking that a woman can't get pregnant by anyone except her husband.) Alternately, Mrs. Meany used the immaculate conception as a flimsy cover story for her affair. This is why Owen and Merrill develop such a close relationship, and why Owen is so determined to find out who Johnny's father is - his second sight lets him know that he and Johnny are half-brothers, so if he finds Johnny's father, he will also find his own.