Levi hails from the impoverished Underground City beneath the capital. After his mother Kuchel Ackerman's death, her brother Kenny found him. Kenny taught Levi survival skills, combat techniques, and the importance of strength before abandoning him. Levi later formed a small group with Furlan Church and Isabel Magnolia, surviving as thieves.

The group attempted to reach the surface by blackmailing Erwin Smith but was captured. Offered a choice to join the Survey Corps, Levi initially intended to assassinate Erwin. However, witnessing the deaths of Furlan and Isabel during an expedition solidified his decision to remain under Erwin's command.

His exceptional combat prowess, speed, strength, and reflexes are attributed to his Ackerman lineage, granting access to dormant combat knowledge surpassing normal humans. Levi quickly earned the title of Humanity's Strongest Soldier and led the Survey Corps' Special Operations Squad.

He operates with extreme efficiency and pragmatism, often appearing detached. A pronounced obsession with cleanliness stems from his squalid childhood. Despite this demeanor, Levi demonstrates deep loyalty and commitment to protecting lives, especially those under his command. Erwin Smith became a central figure Levi respected and followed, viewing Erwin's leadership and vision as crucial for humanity.

Levi endured significant loss. His entire Special Operations Squad, including Petra Ral, perished during the Female Titan incident. Later, severe injuries fighting Kenny Ackerman and the Beast Titan (Zeke Yeager) during the coup to retake Wall Maria resulted in permanent scarring and reduced finger mobility.

His relationship with Eren Yeager was complex. Tasked initially with monitoring Eren due to his Titan powers, Levi acted as a strict mentor and enforcer, willing to use violence for compliance or safety. He later trusted Eren with responsibilities.

Faced with the critical choice to save Erwin Smith or Armin Arlert using the Titan serum during the battle for Shiganshina, Levi chose Armin, believing Erwin deserved rest. This decision haunted him, though he stood by it.

Levi harbored a personal vendetta against Zeke Yeager for Zeke's role in Erwin's death and countless Survey Corps losses at Shiganshina. This vendetta became a primary driving force. Levi captured Zeke during conflicts in Marley and later on a flying boat. Zeke detonated a Thunder Spear while restrained, causing massive injuries to Levi: loss of two fingers, severe leg damage, and facial scarring impairing his right eye.

Despite devastating injuries, Levi survived and recovered over a timeskip. Determined to stop Eren Yeager's Rumbling and fulfill his promise to Erwin to eliminate Zeke, his combat effectiveness was limited. Relying on others for mobility, he confronted Zeke one final time within the Founding Titan's realm. Levi convinced Zeke to sacrifice himself, severing Eren's connection to the Founding Titan via Zeke's royal blood and stopping the Rumbling.

Following the Rumbling's end, Levi was severely injured but alive. He eventually recovered sufficiently to walk with a cane, witnessing the conflict's aftermath. Levi established a tea shop and used his position to advocate for veterans and orphans affected by the wars, finding a new purpose. He remained in contact with surviving comrades like Onyankopon.