The "Monster" of Kinderheim 511 and the antagonist of the series Monster.
Not much is known about Johan's past or even where he came from. He was found at a young age at the border of East and West Germany with his twin sister Anna. The two were placed in different orphanages as Anna was sent to one orphanage while Johan was sent to Kinderheim 511. It was there that he spent his childhood being trained by Neo-Nazis to succeed Hitler and conditioned him to be a relentless leader. As a result, Johan was able to rally the children to kill the guards as he sat on a throne, watching the chaos unfold.
Later on, he is adopted wth his sister by a popular family in Germany, the Lieberts. It was later on after the adoption that Johan killed his surrogate mother and father. Anna confronted him about it with a gun as Johan instructed her how to kill him and what to do with the gun. It is then that Dr. Tenma saves his life by removing the bullet in his brain which ended up ruining his career.
It is unknown as to what Johan's actual name is. While he has kept the surname "Liebert" his first name was given to him by General Helmut Wolfe, who named Johan after a character in a children's book entitled "A Monster Without a Name".
The character of Johan Liebert was created by the original author and artist for Monster, Naoki Urasawa. His anime counterpart was brought to life by director Masayuki Kojima and designed by Kitaro Kosaka.
"Look at me. Look at me. Look at how large the monster inside of me has become."
In the beginning of the series, Johan is presented as a simple child who makes news by being adopted by the Lieberts, a presitgious family that lives in West Germany. It isn't until a buglarly and assault that Tenma meets Johan for the first time. An unknown assailant lodged a bullet in his brain and Tenma has the opportunity to save either Johan or the mayor of Germany. Tenma, feeling conflicted due to his Hippocratic Oath, opts to help Johan and successfully saves his life. However, the mayor dies and this ruins Tenma's career. One night, as Johan is recovering from his operation, Tenma confesses to him that he hopes Johan's life is great since his is ruined. He claims that the chief doctor of the hospital and others are the cause of his demisre. When Johan recovers, the chief of medicine tries to parade Johan around, taking claim for his recovery and gets publicity. However, when he tries to get Anna to take a picture with her brother, she screams in panic and has a mental breakdown. It was after this incident that the enemies Tenma mentioned to Johan each died. Soon after, Johan and Anna disappeared from the hospital. With no leads, the case went silent.
A few years later, Tenma encountered a patient who was a suspect in a string of murders that was occuring throughout Germany. After performing an operation, the patient refered to a Monster and how it was coming. Even though Tenma was able to calm the patient down, he fled immediately once Johan showed up and was killed at his hands. Johan told Tenma that he was grateful that he saved his life and considers him to be like a father to the boy. As Johan leaves, Tenma sees his mistake and all the destruction and death Johan has caused. It is at this point that Tenma makes it his priority to kill the Monster.