Friend

The film follows the lives of four childhood friends: Joon-seok, the leader of the group and whose father is a powerful mob boss; Dong-su, whose father is an undertaker; class clown Jung-ho; and Sang-taek, who was an exemplary student. As children they play together, sell sexually explicit pictures cut from a magazine, and wonder if a South Korean Olympic swimmer could outrace a sea turtle. Jung-ho also showed the rest of them a VCR that his mother had, and this film he found on it. It turns out to be a pornographic movie, and the boys are entranced while arguing over what a "menstruation" was, with them believing that it was the word that adults used to describe the "vagina".Fast forward to high school, where they are reunited after separating during middle school. They become smitten with the lead singer of a band of girls their age. Joon-seok invites the band to a party at his house, where each boy pairs off with one girl (though not after some tension over how to do so). Sang-taek receives his first kiss from the lead singer, Jin-sook.Back in school, Joon-seok and Dong-su get in trouble after a confrontation with a teacher; After their friends convince them to go apologize, they are only off with a light suspension. During an outing to the movies, where Sang-taek catches the eye of another school kid whom he had picked a fight with earlier, Joon-seok and Dong-su fend off a whole rival school while Jung-ho protects Sang-taek. Dong-su, after the fight, returns with a steel rod and smashes the school's glass cases with its awards and trophies, dropping out of school and warning anyone who bumps into him on the street will "pay". Sang-taek is suspended from the affair. After graduation, Sang-taek and Jung-ho go to college but the others do not.A few years later Sang-taek and Jung-ho return to find Joon-seok married to Jin-sook, the singer from the band. He is seriously ill and abusive towards his wife as a result of being addicted to philopon; he also appears depressed that his father is dying. Later he recovers from his illness, divorces his wife, and mourns his father. He assumes his father's role as a crime lord. Dong-su also becomes a mobster with a rival organization, and becomes similarly powerful.Joon-seok, Sang-taek, and Jung-ho remain close, drinking, singing karaoke, and eating galbi together during reunions. After Dong-su causes Joon-seok's boss to be imprisoned, an assassination attempt is led on Dong-su, souring relations and leading to a mob war between the two friends' opposing ganges. After an attack on his men, Joon-seok visits Dong-su at his headquarters. Joon-seok talks to Dong-su as if nothing has happened, and asks if he would like to accompany him to see Sang-taek off, since he was heading to the United States. Dong-su, however, does not want to, and Joon-seok becomes serious. Joon-seok asks Dong-su as a friend to leave for Hawaii for a few years until things cooled down, Dong-su, however, refuses and tells Joon-seok to leave. Joon-seok leaves to say farewell to Sang-taek.What Dong-su did not realize was that Joon-seok asked him to leave as a friend. After mulling over the conversation Dong-su decides to see Sang-taek off at the airport. However, as he is about to leave, Dong-su is betrayed by his gang and stabbed to death.A few years later, Sung-taek returns to South Korea upon finishing his study abroad. Jung-ho explains how during Sung-taek's absence Joon-seok's gang sent him into hiding abroad. After a two years, he was unable to stand the hiding any longer and had a mental breakdown. He was caught after attempting to kill himself in a foreign bar. Joon-seok goes to trial for Dong-su's murder and, even after Jung-ho bribes the jurors, Joon-seok pleads guilty to ordering Dong-su's death, despite his actual innocence.After the trial, Sang-taek visits Joon-seok in prison, and the two talk like old friends who haven't seen each other. When the time comes for Joon-seok to leave to go back to his jail cell, Sung-taek asks why he pleaded guilty in court. Joon-seok simply replies, "Humiliation. Me and Dong-su are mobsters. Mobsters shouldn't be humiliated." Sang-taek and Joon-seok then part ways, with Sang-taek promising to visit every month. The film ends with Joon-seok walking back to his cell, in a hallway with a white bright light in the end, with Joon-seok reflecting on the past when they were all children, wondering who would win in a race, the South Korean Olympic swimmer or a sea turtle, when they were all still friends.

Question: Who is an exemplary student?
Answer: Sang-taek