Wook Pyeon, also known as Mr. Thug, is a former police detective and a resident of Green Roof Apartments.
Wook was formerly a detective for the police, and was responsible for Joon Shin's arrest. He was fired from his job after he used excessive force and nearly killed a suspect.
Wook Pyeon is a tall, athletically built man. He has a fair complexion with short black hair. He frequently wears a sweater and khaki pants.
Due to his appearance, Wook is, to his irritation, mistaken for a thug. Due to his background, he is more aggressive than others, and was fired from his job as a result. He still uses physical force to keep others in line, such as Hyun Cha. Despite this, he means well and will selflessly put his life on the line to save others. He appears confident in his ability to live and doesn't see his acts as a sacrifice, believing he will be able to come back alive. This confidence is borderline reckless: Initially, he preferred to fight monsters barehanded. He has a strong sense of justice and keeps count of the monsters he killed.
Wook is first seen walking around the apartment building, getting annoyed when people refer to him as a "thug." Eventually, he runs into Hyun Cha. He is cautious, as Hyun is armed, and is increasingly suspicious as he notices an apartment has been broken into and the bloody mess as a result. He presses Hyun for answers, but is taken aback when Hyun has a nosebleed and passes out. He hears a commotion upstairs and goes to investigate. While he doesn't see the monster, he sees the aftermath of its attempted break-in. He checks in on Jisu Yoon and the two go check on Hyun. They try to contact security, but after a period of no response, Wook heads to the security office for answers.
At the first floor, Wook notices a crowd and then sees the whole building is shuttered. Seop Anh goes to open the front shutters. As he does so, Wook and the other residents notice a strange man walk up to the entrance. The shutters open and the "man" reveals itself as a monster and begins attacking the residents. Wook and Hyuk Lee fight off the monster, knocking it back outside. Wook reflects on what Hyun managed to tell him and warns the other residents that there may be other monsters already inside the building.
Wook and a small group of survivors eventually figure out monsters will die for good if incinerated. He and a small group of survivors from a rescue party and begin to systemically go floor by floor to exterminate all the monsters. At the Fourth Floor, he and Eun Lee are attacked by the Blind Monster. The two manage to kill it. Hyuk notes the monster's properties, though Wook finds Hyuk's video game-based terms odd. The rescue party continues to climb and clear the building. At some point, they hear the commotion caused by the Tentacle Monster and rush to rescue the survivors: Hyun, Jisu, and Jayhun. They are successful, though at the cost of a rescue party member's life. When Hyun recovers, Wook is mistrustful of the infected Hyun and also is upset at losing a member of the rescue party. Wook participates in the vote over Hyun's fate, though his vote is unknown.
Wook and Hyun are assigned to rescue Dusik Hahn from the 14th floor to enlist his aid in mechanical engineering and improvisational construction skills. He makes it clear that he will kill Hyun without hesitation if Hyun turns. At the fifth floor, he detects a monster and is eager to kill it despite it being completely unrelated to their mission goals. Wook is nearly ambushed by the Hands Monster, but Hyun catches it in time, though getting severely injured in the process. Wook finds the monster's main body and incinerates it. He notices Hyun has quickly recovered. He also advises Hyun that some things, such as the monster's reason for turning, are better left unknown. As they ascend, Hyun becomes increasingly pessimistic and delusional, prompting Hyuk to forcibly knock some sense into him. At the 11th floor, which is a particularly bloodied floor, the two detect an incoming monster. Wook guesses it is the Tentacle Monster and has a simple plan to beat it. They nearly incinerate the monster, but the monster is able to douse the fire and mutate. They only get saved by Seop-Anh and Yuri Park. Wook and Hyun recover in Seop-Anh's apartment, and fall for his prank. The now party of 4 then attempt to ascend; however, they are assaulted by the Speed Monster, who knocks Yuri and Wook unconscious. Wook recovers and helps Yuri recover from an asthma attack. He finds Hyun giving into his monster and beats some sense into him. The party manages to get to Dusik's apartment and carry him down to the lobby.
Wook helps Dusik restore power to the elevators. This forced him to be unavailable to assist in the fight with Mr. Kim, only arriving in its aftermath. Wook then helps and learns about the upgrades Dusik added to the car. Wook is then working at the convenience store, rationing the food, when he is held at knifepoint by a delirious Beyong-Il, who is envious of the more involved survivors. He is forced to accept Beyong-Il's addition to the team for an upcoming mission. At the start of the mission, the group is immediately attacked by the Steroid Monster. They struggle to survive against it, only being saved when it is rammed by a bus.
Wook, however, is displeased to learn their rescuers were prison escapees, including Joon Shin, whom he arrested himself. Joon begins to assert his control over the building while Wook and Hyuk are bound and powerless to do anything. They are left under Hoyoen Kim's watch. Wook challenges Hoyoen to a fight and easily knocks him out, allowing Wook and Hyuk to escape confinement, though Hyuk was infected at this time. The two investigate the bus for supplies, but found the gang had lied about it to gain the advantage. Wook also discovered how the gang was able to avoid monsters for so long: They slaughtered innocent people for bait to distract the monsters. Hyuk then notices a large group of monsters approaching the apartment grounds. The two realize the number of monsters will destroy the barricade. Wook grabs a cooler of human body parts and knocks Hyuk out so that Wook can act as a distraction and lure the monsters away from the main entrance. Wook is able to dodge several monsters and climb into a tree where the monsters lost the trail. Wook notices several Mysterious Cocoons on the ground and sees a monster transforming into one. Then, to Wook's shock, one of the cocoons opens, and it is implied Wook saw a human emerge from it. While greatly unnerved by this, Wook returns to the bus to confront Joon Shin. He manages to get the bus key and kill Joon by throwing him outside and leaving him to the monsters. Wook then barricades the front entrance with the bus.
Wook grabs the shield Dusik made and escapes the bus with Meyong-Il. He runs to the garage, the only open entrance to the building, just in time to save Hyun from a monsterfied Dusik. Wook insists on taking over the fight, not wanting a kid like Hyun have to go through the pain of killing a friend. He then turns his attention to Dusik, and after some effort, manages to pin him to the ground, letting the flames in the burning garage consume him. Wook tells Hyun what he has been doing, but also wonders what good is surviving if people have to be sacrificed.