Main

• Lee Min-ho as Lee Yoon-sung / Poochai
  • Chae Sang-woo as young Yoon-sung / Poochai

Codenamed "City Hunter", Yoon-sung's ultimate goal is to avenge his father's killers. Using the identity of a Korean-American teenager named John Lee, who is later revealed to have died several years before, he assumes a double life by graduating from MIT with a doctorate degree and lands a job at South Korea's presidential palace. It led him to cross paths with presidential bodyguard Kim Na-na, with whom he falls in love. Unlike Jin-pyo, Yoon-sung does not desire taking lives and only hopes to bring the five murderers to justice by exposing their crimes and sending them to prison, which often made him go into conflicts with Jin-pyo, who wanted to kill the five men.

• Park Min-young as Kim Na-na

Forced to take care of herself at an early age after her mother was killed in a drunk driving crash and her father became comatose (Na-na's father never regained consciousness and he eventually passed away in the end of the series), she is independent and strong-willed. Her exceptional skills in martial arts eventually earns her an assignment with the Presidential Security Service. During her time as a bodyguard, she falls in love with Lee Yoon-sung and eventually discovers his real identity.

• Lee Joon-hyuk as Kim Young-joo

An intelligent prosecutor, Kim Young-joo possesses a strong sense of justice, even against the corrupt politicians of South Korea. He is the son of one of the members of the "Council of Five", and was ashamed of his father for his corruption and cover-up of the crash that killed Na-na's parents. Out of guilt, he helped Na-na to complete her education and ensure her stable employment as a bodyguard. He is a constant rival of City Hunter, working towards the same goals under legal cover, while trying to figure out his identity at the same time. He was later ruthlessly killed by Jae-man and his henchmen before he could arrest him, and before he died, he pleaded with Yoon-sung to forgive his father for his crime.

• Kim Sang-joong as Lee Jin-pyo

Operation Clean Sweep's sole survivor, Lee spends the mediate years in the Golden Triangle as a drug lord. Full of anger, he wants to kill all of the people who ordered his team dead. Under the alias Steve Lee, Jin-pyo pretends to be a Korean-American investor and uses Lee Yoon-sung as his agent of vengeance. Originally a good-natured person, he was gradually depicted as a murderous and merciless man who would do anything to achieve his goals of vengeance and had even targetted innocent people who got into his way. His notable victims include two of the "Council of Five" members: Lee Kyung-wan and Chun Jae-man.

• Kim Sang-ho as Bae Man-duk / Bae Shik-joong

A problem gambler but a very good cook whom Lee Yoon-sung saves from thugs in Thailand and later becomes his close friend. Over the course of the series, Bae and Lee become partners under Lee Jin-pyo's scheme – and also racks up huge debts buying stuff from the home-shopping network. However, it is revealed that Bae witnessed the crash that resulted in Kim Na-na's woes and was hiding in Thailand by the start of the series after being paid off by the culprit – Kim Jong-shik, a member of the Council of Five – to change his story. He regretted the cover-up despite having done it, and had wanted to make amends with Na-na, which he eventually did and Na-na also eventually forgave him.

• Hwang Sun-hee as Jin Sae-hee

A veterinarian by trade, Sae-hee is Young-joo's ex-wife and a good friend to the other characters. She is the first of Lee Yoon-sung's accomplices to learn of his secret identity as the City Hunter.

• Goo Hara as Choi Da-hye

One of President Choi's two children, Da-hye is smitten with Lee Yoon-sung early in the series and requests him to be her tutor. Her status of being the president's daughter does not win her any friends at school and even creates a public scandal when she attacks a group of girls who criticizes her father's governance within earshot. She decides not to go to college (because of her poor grades) and is forced to find a job, and later falls in love with Kim Young-joo. It was later revealed that she was Yoon-sung's biological half-sister, with the revelation of Yoon-sung's blood link with Choi.

• Chun Ho-jin as Choi Eung-chan

The incumbent president of South Korea, Choi was one of the five men involved in planning the 1983 operation and promised the unit he will help get them home. He was later out-voted in the decision to abort the operation and forced to live with the guilt for 28 years. He is the only member of the group who knows that Lee Jin-pyo survived the debacle, yet does nothing to stop him despite knowing that the former bodyguard's ultimate goal is to kill him and the other officials. It is later revealed that the president is Lee Yoon-sung's real father, who sired him with Lee Kyung-hee. He is depicted in the series as an idealist who believes the end is worth the means, which results in his impeachment by the National Assembly after he bribed a number of deputies to help pass an important education reform bill.

Supporting

• Park Sang-min as Park Moo-yeol

Lee Yoon-sung's father, who dies protecting Jin-pyo in the first episode. It is revealed that he is not Yoon-sung's real father, and was merely protecting Lee Kyung-hee after her affair with Choi Eung-chan ended. Park and Lee Jin-pyo's names are at the top of a memorial slab honoring the Clean Sweep team.

• Kim Mi-sook as Lee Kyung-hee

Lee Yoon-sung's mother, who went on to lead a solitary life running a small eatery after Yoon-sung was kidnapped as an infant. She had become pregnant with Choi Eung-chan's child, but when she decided to keep the baby, her life and the baby's was threatened by Chun Jae-man. She contracts leukemia later in the series, but starts to recover after Yoon-sung donates bone marrow to her. Kyung-hee travels to the United States with Shik-joong to start a new life in the final episode. Initially misled by Jin-pyo's lies, Yoon-sung believed that his mother abandoned him, until the truth came out.

• Lee Seung-hyung as Song Young-duk

The head of the Blue House's National Communications Network team.

• Yang Jin-sung as Shin Eun-ah

Kim Na-na's other female colleague in the PSS, who is assigned to look after Choi Da-hye.

• Lee Kwang-soo as Ko Ki-joon

Yoon-sung's colleague in the National Communications Network team who is visibly interested in Eun-ah. The couple are engaged at the end of the series. Ki-joon has a younger brother who served in the military but was crippled due to Seo Yong-hak engaging in corruption by supplying the military with poor quality boots, which caused Ki-joon's brother to suffer from a permanent leg injury.

• Jung Joon as Kim Sang-gook

A former police officer, Kim is tapped by Jin-pyo for the revenge project upon learning that his own brother was part of the 1983 operation. He was sacked from the force for breaking into the National Intelligence Service's files while trying to find out what happened to his brother. Eventually, after seeing Jin-pyo's true self and disagreeing with his extreme methods of revenge, he switched his allegiance to Yoon-sung and secretly helps him in the later part of the series.

• Lee Hyo-jung as Lee Kyung-wan

A senator, Kyung-wan is the City Hunter's first target among the Council of Five, who also pocketed certain children's welfare funds. He is imprisoned for the crime, but is implied to have died at Jin-pyo's hands in episode 9.

• Choi Jung-woo as Chun Jae-man

A businessman running a chaebol (a chemical company and hospital is seen in the series as part of it), Jae-man participated in planning the North Korea mission. He is the most corrupt and ruthless member of the Council of Five. He later burns a book containing all covert operations in 1983 that were supposed to be declassified in 2030. It is revealed that the book he burned was just a copy and Jin-pyo acquired the original document, but not before Jae-man does a little historical revisionism by saying that the operation took place because the team tried to defect to the North with some state secrets. His corruption case is also depicted as one that no government prosecutor wants to handle, as those who do take it on are often harassed into quitting. Chun dies at Jin-pyo's hands in the final episode.

• Choi Il-hwa as Kim Jong-shik

Kim Young-joo's father and a former education minister, Jong-shik was one of the officials who plotted the North Korea mission and agreed to the subsequent cover-up. He also killed Kim Na-na's mother and gravely injured her father while drunk-driving, and pays off a witness (Bae Shik-joong) to say that Na-na's parents were at fault for the crash. He showed no remorse of his crime, which made him even in odds with his son. He would become comatose later in the series as the City Hunter tries to take him down in light of an investigation over hiding around two billion won in college subsidies. He regains consciousness in the final episode to learn of his son's death.

• Choi Sang-hoon as Seo Yong-hak

A former defense minister and a prospective presidential contender, Yong-hak was an army general at the time of the 1983 operation and has often used his influence to have his three sons avoid the military's required three-year conscription. The City Hunter unmasks him for entering into deals to provide substandard combat boots and acquire defective fighters for the Air Force. As the truth behind Clean Sweep unravels, Yong-hak comes forward with what he knows and pins the president as the mastermind.

Special appearances

• Min Young-won as Min-hee
• Yoon Ye-hee as Mrs. Yong (First Lady)
• Kim Byung-choon as Jang Woo-hyun
• Shin Young-jin as Kim Mi-ok
• Kai Supranee as supporting Thai actress

Part 1

Part 2

Part 3

Part 4

Part 5

Part 6

Part 7