Levi is the son of Kuchel Ackerman, a prostitute who worked in the Underground and was made pregnant by one of her clients. One day, Kenny Ackerman, Kuchel's older brother, came to the city to see her only to find that she was dead.[25] There, he found a young and squalid Levi sitting in front of his mother's bed.

In a rare showing of compassion, Kenny decided to take care of him. He raised Levi as well as he could: teaching him knife skills, how to get along with people, and violent behavior. Levi also learned to use his own inner power that he possessed as a member of the Ackerman clan.[26]

Following his mother's death, Levi attempted to steal back a tea set she had sold in order to pay for food. He was caught in the act and the merchants, after apprehending him, considered selling him into slavery. Levi, disgusted by their behavior, attempted to resist and was nearly beaten to death. However, before the merchants could finish him off his Ackerman blood awakened and he killed all of them in a moment of blind rage. After calming down, he was confronted by the sole surviving merchant who attempted to blackmail Levi into sparing his by arguing that his friends would hunt Levi down and kill him in retribution unless he left the merchant alive to talk them down. Levi simply retorted that no one would believe that a child had killed them before throwing the merchant to his death.

Returning to his home, Levi made himself a cup of tea using her set. However, when he attempted to drink it the handle broke, causing him to drop and shatter the cup. From that point on, Levi refused to hold cups by their handles, choosing to hold them by their brims instead.[27]

Time passed and eventually, Kenny taught Levi everything he knew. However, he did not consider himself as a good father figure.[28][29] One day, in the subterranean city, Levi started a fight which he won easily. At that moment, Kenny decided to leave him behind, satisfied that he had taught Levi the skills he needed to survive.[30]

Later, he became a notorious thug in the underground but eventually left the place to join the Survey Corps.[3] Although he was at odds with Erwin,[31] he ended up becoming one of his most trusted men.