Nile Dok was the former commander of the Military Police Brigade, Erwin Smith's childhood friend, husband of Marie Dok and father of three daughters.
Zeke Yeager transformed Nile into a Titan when the Marleyan military launched a counter offensive on Shiganshina.
As a human, Nile was a lean man with well-defined cheek and jaw bones. He had thin black hair that was cut shorter on the sides but was relatively shaggy elsewhere. Nile's eyes were notably narrow and dark, with mild bags beneath them. He also sported a very light mustache and goatee. He was always seen wearing the standard military uniform bearing the Military Police symbol, paired with a bolo tie similar to that of his fellow military commanders.
Appearance: As a human, Nile was a lean man with well-defined cheek and jaw bones. He had thin black hair that was cut shorter on the sides but was relatively shaggy elsewhere.
Personality: Nile prided himself on being a very rational individual. Whenever he was faced with a tough choice, he weighed all possible options and chose the one that made the most sense to him.
History: Nile was a member of the same Training Corps as Erwin Smith, and the two were good friends. They agreed to join the Survey Corps together, but then Nile met a woman named Marie at the bar the group often frequented.
Nile Dok in the story: Nile first appears as the leader of the Military Police during the trial of Eren Yeager. He advocates killing Eren due to the impending civil war, but he does analyze and weigh the different pros and cons of Eren before making his final decision. He recognizes that Eren's Titan powers had saved Trost District, but threaten the balance of power within human society.
Source: Attack on Titan Wiki, available under CC BY-SA 3.0.