The Priest was a Silencer that lived in and operated from the caverns outside Urbania. After the 3rd Wave, he lived amongst all the other gathered people there. He would lead them in prayers and offer solace to anyone in fear and doubt. Yet, he went and 'silenced' anyone that started to cause trouble or gave him a hard time and would dump their bodies in a pit. He kept this going until he was the only one left in those caverns.
At a time during the 3rd Wave, the Priest was overlooking the caves that he was staying in along with a good collection of people when he stumbled on one of them having a smoke outside. They started sharing some words about faith which the smoker said that he used to have faith and believed in things. How he believed that the lights would come back on, or how he believed that the west and east coastlines would always be where they were and that when you were sick then you would get better with time and medicine but not anymore since The Others came. Eventually, the Priest went and killed this man and then dumped his body in a pit with other corpses as he secretely longed for when the 5th Wave would be utilized.