Levi Ackerman is a central figure in the military’s Survey Corps, serving as captain of the Special Operations Squad and known as humanity’s strongest soldier.

He has short, straight black hair in an undercut, narrow and intimidating steel-blue eyes with dark circles beneath them, and a deceptively youthful face. His stature is notably short, but his body is well-developed from extensive use of vertical maneuvering equipment. He typically wears the standard Survey Corps uniform with a light gray button-up shirt and a white ascot, though he later stops wearing the ascot. After a close-range Thunder Spear explosion, he sustains significant facial scarring, including a mark across his right eye, and loses the index and middle fingers of his right hand. A later fall from a great height results in his confinement to a wheelchair.

He is intensely focused on cleanliness, earning him the nickname "clean freak." He displays a strong aversion to dirt on his person or equipment, though he will ignore this if the situation demands it. His demeanor is generally cold, abrasive, and unapproachable, marked by minimal emotional expression, blunt and often insulting speech, and a dark, vulgar sense of humor. Beneath this exterior lies a strong moral compass and deep empathy, particularly for human life. He cares profoundly for his subordinates and is deeply affected by their losses.

He offers obedience only to those he respects, such as Commander Erwin Smith, and shows open disdain for other authority figures. He operates with significant independence and is capable of extreme ruthlessness and sadistic behavior toward enemies he perceives as threats to humanity. Despite his renowned combat skills, he displays no arrogance.

Levi was born in the Underground City to a prostitute named Kuchel Ackerman. After her death, he was raised by his uncle, Kenny Ackerman, who taught him survival skills, knife fighting, and violent behavior. This training also triggered the awakening of the Ackerman clan's unique power. Kenny eventually abandoned him, confident he could survive alone.

Levi later became a notorious thug in the Underground, forming a gang with Furlan Church and Isabel Magnolia. They used stolen vertical maneuvering gear to perform heists and were coerced by a surface man, Nicholas Lobov, into joining the Survey Corps with the goal of assassinating Erwin Smith in exchange for surface citizenship. During their first expedition beyond the walls, both Furlan and Isabel were killed by Titans. This event became a turning point, leading Levi to follow Erwin and dedicate himself to the Survey Corps, leaving his criminal past behind.

In the main story, Levi is entrusted with the protection and oversight of Eren Yeager, forming a special squad for this purpose. He suffers a leg injury during a confrontation with the Female Titan, temporarily sidelining him. He carries the will of fallen comrades, which strengthens his resolve to fight. A significant rivalry develops with Zeke Yeager, following a final order from Erwin Smith to kill him. Levi eventually succeeds in killing Zeke, fulfilling this promise, but not before suffering severe injuries from a Thunder Spear explosion engineered by Zeke.

His development shows a shift from someone who cared only for his closest comrades in the Underground to a leader who values the lives of his subordinates deeply, though he does not see himself as a conventional leader. The repeated loss of comrades, including his original squad and his uncle Kenny, affects him profoundly and reinforces his commitment to his cause and those under his command.