Pastor Nick is a minor antagonist in the Attack on Titan series. He's the leader of the Wall Cult, and has halted any kind've developed on the Walls.
Nick claims that he lost his family due to alcohol addiction at a young age. Some time later, Nick became the leader of the Wall Cult, a religious sect that believes the Walls are the creation of God. Using his influence, Pastor Nick has halted any can of development on the Walls, claiming that it's blasphemy to "maim" the Walls.
Nick is seen at the Trial alongside Erwin Smith, Dot Pixis, and Nile Dok to decide what should be done with Eren Jaeger. He pleads that Eren be executed, due to his Titan powers, and how unstable he and most of the military police thought Eren was.
Nick can later be seen holding a gathering in the Stohess District, praying to the Walls for guidance. But his congregation is killed, after Eren punched Annie into the temple he was in. Nick survives, and pleads with the Military to cover up the holes Annie was created in the Walls, possibly to cover up anything having to do with the Wall Titans or to not in any way let any other titans in. Possibly relating to the Colossal Titan as well.
Realizing Nick knew about the Titans, Hange tries to press Nick for information. He refuses, and she tries to throw him off the Wall. He responds by claiming he's a sinner, and that he should divulge his secrets.