Zackly 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. He often wears a brown trench coat that has a black shield emblem with a white border and cross.
Zackly is said to be a strict military leader who is only concerned with the best interests of humanity. As the head of the entire military, his priorities are said to lie within what is best for all of humanity.
In a flashback, Zackly is seen in his office discussing with Keith Shadis 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 Survey Corps use the formation, arguing that the major anti-Survey Corps opinion within deputies would not allow it. In addition, Zackly reminded to an angry Keith that the dissolution of the Survey Corps would be decided in five days.
Later on, Zackly announced to Keith and Erwin the assembly voted to maintain the Survey Corps. 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, Zackly accepted.