The Mousetrap cast is led by Ryu Jun-yeol as reclusive novelist Je Moon-jae, Sul Kyung-gu as ruthless loan shark No-ja and Lee Kyu-hyung as detective Park Sun-yong. The Netflix thriller turns identity theft into a battle over a person’s face, history and legal existence—and its most important casting decision is giving Ryu two sharply different versions of the same appearance.
This guide explains who plays whom without revealing the series’ final answer to its central mystery. Viewers who have completed all 10 episodes will find a link to our spoiler-filled identity and ending analysis at the end.
Mousetrap cast at a glance
| Actor | Character | Role in the story |
|---|---|---|
| Ryu Jun-yeol | Je Moon-jae / The Rat | A novelist and the doppelganger who takes over his identity |
| Sul Kyung-gu | No-ja | A loan shark and private investigator who joins the hunt |
| Lee Kyu-hyung | Park Sun-yong | The detective following the identity-theft case |
| Kim Sung-oh | Park Seung-gyu | A dangerous figure connected to the wider conspiracy |
| Lee El | Han Ji-hye | Moon-jae’s longtime editor |
| Park Yoon-ho | Seo Yu-min | A man from Moon-jae’s past |
Ryu Jun-yeol plays Je Moon-jae and The Rat
Ryu Jun-yeol carries the drama’s central illusion. Je Moon-jae is a successful suspense novelist whose panic disorder has kept him inside his home for years. When his phone stops recognizing his fingerprint and the person who managed his daily life disappears, he discovers that someone has taken his name, money, records and public credibility.
The actor also appears as the immaculate doppelganger known as The Rat. The two men share a face, but Ryu distinguishes them through posture, eye contact and speech.
Moon-jae looks as though every encounter costs him energy; his double moves through the world with the ease of someone who expects to be believed. The performance makes the theft feel physical before the plot explains how it happened.
Ryu became widely known through Reply 1988 and later led films including The King, A Taxi Driver, Money and the two-part Alienoid. Netflix viewers may also recognize him from The 8 Show. Mousetrap uses both his nervous intensity and his ability to become unexpectedly unreadable.
Sul Kyung-gu plays No-ja
No-ja is more than the violent creditor introduced at the beginning. He runs a private investigation business, understands the hidden economy behind false documents and has spent years looking for Moon-jae over an unpaid debt. Recovering that money gives him a practical reason to join the writer’s search for The Rat.
Sul Kyung-gu gives the character a calm that is often more threatening than shouting. No-ja can treat Moon-jae as a client, hostage and reluctant partner within the same conversation. Their alliance supplies much of the series’ dark humor, but it also prevents the isolated novelist from facing the conspiracy alone.
One of South Korea’s most respected film actors, Sul has appeared in Public Enemy, Oasis, Memoir of a Murderer and Netflix’s Kill Boksoon. He also led the political drama The Whirlwind. His presence gives No-ja the weight of a man who has survived long enough to distrust every version of the truth.
Lee Kyu-hyung plays Detective Park Sun-yong
Detective Park Sun-yong investigates the trail left by Moon-jae, No-ja and the identity-laundering operation. At first, he appears to be the official counterweight to two men working outside the law. As the case becomes more personal, however, Sun-yong’s own history begins to matter to the mystery.
Lee Kyu-hyung is especially effective at playing characters whose composure hides emotional damage. Viewers may know him as Yoo Han-yang in Prison Playbook, from the fantasy drama Hi Bye, Mama!, or through supporting roles in Stranger and All of Us Are Dead. Here, his controlled performance keeps Sun-yong credible as a detective while allowing doubt to accumulate around him.
Kim Sung-oh plays Park Seung-gyu
Park Seung-gyu connects the central chase to the criminal network operating around stolen identities, debt and violence. He is not simply another obstacle placed between Moon-jae and the truth. His decisions show how much money and protection are required to erase one life and build another.
Kim Sung-oh is a familiar presence in Korean thrillers and action stories, with credits including The Man from Nowhere, Fight for My Way and Money Heist: Korea – Joint Economic Area. His ability to shift between menace and dry humor fits a series in which alliances can change from one episode to the next.
Lee El plays Han Ji-hye
Han Ji-hye is Moon-jae’s longtime editor and one of the few people capable of confirming who he was before the theft. That makes her professionally useful and personally dangerous to everyone invested in replacing him. Her history with the novelist also reveals how thoroughly his isolation allowed other people to control access to his public life.
Lee El brings an intelligent reserve to Ji-hye. The actress is known internationally for Guardian: The Lonely and Great God, My Liberation Notes and the thriller film The Call. In Mousetrap, even a simple statement from her can alter which version of Moon-jae seems believable.
Park Yoon-ho plays Seo Yu-min
Seo Yu-min belongs to Moon-jae’s university past and becomes increasingly important as the writer recovers fragmented memories. Explaining more would spoil one of the drama’s major turns, but Yu-min is essential to understanding why the crime is not motivated by money alone.
Park Yoon-ho plays the younger Yu-min, allowing the series to show the relationship before years of resentment and retaliation changed everyone involved. Song Sui appears as So Min-young, another key figure from that period whose story helps explain the emotional cost behind the central scheme.
Other supporting actors in Mousetrap
The supporting ensemble includes Mu Jin-sung as Son Soo-hyun, Hong Ki-joon as Min-gi and Hyun Bong-sik as Kang Myeong-su. Jung Hee-tae plays police officer Kim Han-su, while Lee Kwan-hoon, Shin Soo-ho and Lee Chan-yong appear as other members of the Dongbu Police Station team.
These characters matter because the conspiracy could not work through one impostor alone. Lawyers, brokers, police officers, creditors and people from Moon-jae’s past each hold a different piece of his identity. The large cast turns a personal nightmare into a system in which official records can become more convincing than memory.
Why Ryu Jun-yeol’s dual role works
The drama asks viewers to compare two men before they know which details can be trusted. Using Ryu Jun-yeol for both present-day faces makes every difference in behavior meaningful: one avoids attention, while the other knows how to perform confidence; one struggles to speak for himself, while the other has already mastered the story he wants the world to believe.
Sul Kyung-gu and Lee Kyu-hyung then pressure that performance from opposite directions. No-ja tests identities through money and criminal knowledge; Sun-yong tests them through evidence and police procedure. Together, the three leads give the 10-episode thriller its changing balance of suspicion.
Mousetrap is streaming globally on Netflix as a 10-episode limited series. The drama is based on Ludovico’s Kakao webtoon Field Mouse. Viewers who have finished the series can continue with our spoiler-filled explanation of Mousetrap‘s ending and the real impostor.