Nick, often formally referred to as Minister Nick, was a high standing, devoted member of the Church of the Walls, a religion that worships the Walls and considers them to be holy.
Nick was a very tall man and older looking with noticeable wrinkles on his forehead and around his eyes, which had dark circles over them. His hair was high up on his head and was parted to the left, with the sides and back being much shorter. He wore a black cassock with three bands near the top that had the symbols of the Walls.
Nick could be characterized by the word extreme. Any attempt to interfere with his mission or the Walls was a sin and considered the worst possible offense in his mind. He never hesitated to make his opinion known and was extremely quick to condemn anyone who disagreed with him. This was displayed at the trial of Eren Yeager where he loudly called for his execution and publicly argued with a merchant who suggested sealing the Walls. Any viewpoint besides his own was considered sinful and horribly wrong.
Appearance: Nick was a very tall man and older looking with noticeable wrinkles on his forehead and around his eyes, which had dark circles over them. His hair was high up on his head and was parted to the left, with the sides and back being much shorter.
Personality: Nick could be characterized by the word extreme. Any attempt to interfere with his mission or the Walls was a sin and considered the worst possible offense in his mind.
History: Nick claimed that he lost his family as a result of his addiction to alcohol. As a religious leader, Nick used his influence to oppose any modification of the Walls, be it permanently sealing the gates or even mounting cannons on the top.
Nick in the story: Minister Nick first appears at Eren Yeager's military trial. He and Nile Dok advocate for Eren's execution because of the danger his power poses. During the trial, a merchant suggests permanently sealing Wall Rose to stave off another Titan attack, enraging Nick.
Source: Attack on Titan Wiki, available under CC BY-SA 3.0.