Johan grew up with only his mother in a poor neighborhood. Johan's mother supports Johan by working as a hair cutter in her own hair salon. His mother is slowly losing her eyesight due to an illness and she lost many customers because of it. Johan was often bullied at his junior high school.
Johan has brown hair and black eyes. He is shown to have a slender but lean physical build.
Johan is first introduced as a timid child, who is in love with Mi Jin, just like Jin Sung. He is shown to care more for others than for himself, as he allows himself to be beaten by bullies in order to avoid getting in trouble for the sake of his mother. When he was younger, he was very obedient and cared dearly about his mother and Mi Jin.
In the plot, he is very religious and it is shown to always have gone to church with his childhood friends Mi Jin and Jin Sung. His mother after a period of time lost her sight and while losing her sight she entered a cult. His mother rants about being one of the chosen for the "Dog God" and drags Johan, his church priest, Mi Jin and Jin Sung in to the cult where the latter and Johan discover a man crucified on a cross. They worked together untying the person on the cross and it was later revealed that he was a reporter that wanted to write an article about the illicit dog cult. It was later revealed that the priest that accompanied them in the beginning was the founder of the religion.
The priest seized this opportunity as soon as they were about to escape by grabbing Mi Jin, then calling out his guard dogs leaving Jin Sung and Johan greatly outnumbered. The reporter ran away from the scene leaving the three. Johan and his friends were all locked inside dog cages forced to watch the sacrifice while the priest. Johan's mother (with her poor eyesight) regained her sanity after seeing Johan in the cage with her poor vision. The priest caught Johan's mother after she unlocked the cage commanding his disciples to use her as a sacrifice for the dog gods. The priest unlocked the cage Mi Jin was inside and dragged her by the hair into the warehouse.The main worshipper took Jin Sung and Johan out of the cages with their hands tied to watch the sacrifice upclose.
The disciples gathered around Johan's mother with stones and began chucking them at her, but before any rock landed on her, Johan directed the rocks away from his mother with quick jabs he learned from Jin Sung. It was revealed that Johan got out of his handcuffs by repeatedly grinding it against his skin in order to slip out of them.
Johan rescued his mother and went with Jin Sung to save Mi Jin. Cutaways ensued showed that the priest used hallucinogens to convince Johan's mother to convert herself away from Christianity. Johan and Jin Sung fought their way towards Mi Jin. However, the priest was guarded by his dogs and had a bucket of meat to coax his dogs. Since Johan and Jin Sung were stuck at an impasse, they were hesitant. Mi Jin then bit the priest in the leg buying enough time for Johan's mother to suddenly douse the priest in meat grease, which lured his dogs to eating him alive. The reporter from earlier called the police and took over the case. Johan's mother was taken to a rehabilitation center leaving Johan alone once more.
Afterwards, he goes missing only to show up during the boxing completion that Jin Sung was also participating in. He unexpectedly beats Jin Sung and once again disappears.
The next time he appears in the story he get a hair cut from his mother and after that is seen walking with Jong Gun, talking about Johan being Gun's "Successor".
Johan is a member of the fearsome Big 4 Crew and is the leader of one of it's main 4 Crews The Dog God Crew. Johan's true potential was always held back because he did not want to cause trouble for his mom by fighting. However he finally decided to accept his potential in order to save his mom from being stoned to death.
Much like Park Hyung Suk, Johan also is the only other character in the series so far who has been shown to have the ability of executing a technique down to its mechanics just from a single glance. This is shown when Johan learned Jin Sung's jabs and was able to perform them with great skill after a single look. A few years, later it would be that very technique he learned from watching Jin Sung that he uses to save his mom's life. However unlike Park Hyung Suk he seems to stick with the first fighting style he learned (Boxing from Jin Sung) and has only improved upon it, whereas Park Hyung switches between various fighting styles to better suit himself in a fight.
Johan uses the same fighting style as Jin Sung in boxing. He heavily relies on speed and burst power to strengthen the force of his punches. Johan's talent even surpasses Jin Sung, someone who has trained since he was young in boxing. He is faster than Jin Sung as stated by many characters and was the first to beat Hyung Suk in a race (albeit he had ran 3 miles prior to their race). He defeated Jin Sung in a boxing match, for his punches were too fast for Jin Sung dodge.
Johan's strength is not to be taken lightly, despite his athletic build seemingly more suited for speed. Johan can unleash all his energy in a single moment creating immense burst power and strength with enough force to forcefully open a locked steel door. He has also been shown beating Park Hyung Suk in a race. Jong Gun, a legendary fighter, later chooses Johan to be his successor.
Johan yearns to be Jong Gun's successor, as he seems to wish for Jong Gun's $5,000,000 salary, which he presumably wants to support his mother.