Nick

Pastor Nick is a member of a religion that worships the Walls as holy.

Background
Pastor Nick claims that he lost his family as a result of addiction to Vine.

As a religious leader, Pastor Nick used his influence to oppose any modification of the walls, be it permanently sealing the gates or even mountaing cannons on the top. Though he claimed it was blasphemy for humans to "maim" the wall, the real reason was to reduce the risk of workers discovering the Titans within during renovations.

Story
Pastor Nick first appears in Ch. 19, when he advocates for the execution of Eren upon the revelation of Eren's ability to transform into a Titan.

In Ch. 34, when Annie Leonhardt breaks a portion of Wall Sina and exposes a Titan within, Pastor Nick orders that it be covered up immediately to prevent the sunlight from awakening it. Realizing that Pastor Nick knew the truth about the Titans within the Walls the entire time, Hanji Zoe threatens him in an attempt to get him to reveal more, but he refuses.

In Ch. 37, Hanji brings Pastor Nick with her through the Hermiha District so he can see the suffering of the families forced to evacuate because of the suspected breach of Wall Rose. While he will not himself betray the secrets of his organization, he tells the group about a girl, hiding under an assumed name, who would be able to speak about the secrets. Eren and the others realize Pastor Nick is speaking about Christa Renz.