Zachary has the typical appearance of an old man. His eyes are sunken and tired-looking, he wears glasses, he has noticeable wrinkles on his face, and his hair is receded and gray. He also has a gray scruffy looking full beard and mustache. In addition, he is rather short which gives him a presence uncommon for a man of his rank. Zachary's casual attire consists of a plain white shirt with normal dark colored pants. In a more formal setting he adds a bolo tie, much like the three commanders under him, Nile Dawk, Erwin Smith, and Dot Pyxis. Over this he wears a brown trench coat that has a black shield emblem with a white boarder and cross.
When he was first introduced, Zachary was said to be a strict military leader who was only concerned with the best interests of humanity. As the head of the entire military, his priorities were said to lie within what is best for all of humanity. Only after being logically convinced of Eren's usefulness did he pardon him. At this time he appeared to take most things lightly, as if he had experienced them previously. During the trial of Eren he wore simple clothes and conducted the trial without any drama or passion. Similarly, he overthrew the monarchy with an incredibly casual demeanor. This indicates that Zachary has no time for drama and is solely focused on carrying out his judgments. He remains ever serious but at the same time appears tired as if his age is catching up to him.
According to Armin, Zachary is among the people capable of abandoning their humanity to outdo the Titans as well as having the guts to also abandon things important to them in order to change something in the world, along with Erwin Smith, Ian Dietrich, and Dot Pyxis.
In a flashback, Zachary is seen in his office discussing with Keith Sadies and Erwin Smith about the Long-Distance Enemy Scouting Formation Erwin had created. While finding it ingenious and agreeing with its concept, he nevertheless refused to let the Scout Regiment use the formation, arguing that the major anti-Scout Regiment opinion within deputies would not allow it. In addition, Zachary reminded to an angry Keith that the dissolution of the Scout Regiment would be decided in five days.
Later on, Zachary announced to Keith and Erwin the assembly voted to maintain the Scout Regiment. Noting that it will not probably be the case next time, he urged them to do their best. Erwin then asked him about a request he formulated earlier which consisted in going to the Underground in order to recruit a gang of thugs, putting the emphasis on their outstanding skills. Interested in Erwin's sayings, Zachary accepted.
Zachary first appears when Eren Jaeger is put on trial. He confirms who Eren is and then announces that the sole right of judgement rests with himself. Eren will either survive and go with the Scout Regiment, or he will go the Military Police Brigade and be killed.
Zachary calms Minister Nick down after he called for Eren's immediate destruction and then offers Erwin the chance to speak. The latter expresses his plan to use Eren's powers to retake the Wall Maria. A merchant and Levi then argue about the sealing of the gates. Nick interrupts again and begins arguing with the merchant, prompting another call for order from Zachary. Zachary asks if Eren can use his powers for good, Eren replies yes and Zachary counters that Eren reportedly attacked Mikasa Ackermann, another soldier. She reluctantly admits that he did attack her but also requests that it be taken into consideration that Eren saved her life twice before that. Nile disagrees with this by citing an incident from Eren's past where he stabbed two robbers. Eren begins to get angry and is pointed guns at by the Military Police but Levi arrives and begins to beat him.
Erwin then offers a proposition to Zachary: the Scout Regiment will take Eren and assess his usefulness to humanity and if anything goes wrong, Levi will kill him. Zachary agrees with this deal and announces that Eren will join the Scout Regiment and return to trial after his ability has been assessed.
As commander-in-chief he is the highest authority within the military structure. The three military divisions, the Garrison, the Military Police, and the Scout Regiment are all officially under his command, despite having their own leaders. In matters of military law he is the sole decision maker that cannot be argued against. Within the context of a Military Court, he has the power to condemn the defendant to death if he chooses.