Seo Kang-joon spent a decade being cast for his face. A spy comedy changed the question

Seo Kang-joon

Photo: 티비텐 TV10 / CC BY 3.0, via Wikimedia Commons

Born	October 12, 1993 Gunpo, Gyeonggi Province, South Korea
Occupation	Actor
Known for	The Beauty Inside, A Year-End Medley
Awards	MBC Drama Awards · 2 KBS Drama Awards · Korea Drama Awards

On the night he collected the biggest prize of his career, Seo Kang-joon barely talked about winning. He talked about being replaced. Holding MBC’s grand prize for Undercover High School, he told the room that he had missed film sets badly while he was in the army, and that during the shoot he kept thinking someone could take his place at any moment. He did not want that to happen, he said, until the day he finished. It was a strange confession from an actor whom Korean television had cast for a decade on the strength of a face that sold dramas before anyone asked whether he could carry them.

Seo was born Lee Seung-hwan in Gunpo, a commuter city south of Seoul. He spent about a year and a half of his middle-school years studying in Malaysia, and he was working as a part-time model when the agency Fantagio signed him. Fantagio was then putting together 5urprise, a five-man group of young actors who also released songs, a training format that pushed new faces onto variety shows and web series well before any of them had held a scene. He later studied performing arts at Dong Seoul University.

He was born on 12 October 1993, so the first credits arrived when he was still 19, and they are small: a supporting part in SBS’s The Suspicious Housekeeper, a long run on the reality show Roommate, a son in the KBS weekend family drama What Happens to My Family?. The first proof that he was more than decoration came with Cunning Single Lady, the MBC romantic comedy that won him Best New Actor at the Korea Drama Awards.

Then came Cheese in the Trap, tvN’s adaptation of Soonkki’s campus webtoon, in which he played Baek In-ho, the quick-tempered former piano prodigy whose injured hand had closed off a career. The role made him famous, and it also placed him inside an argument he had not started. In its second half the series drifted away from its nominal male lead, Yoo Jung, played by Park Hae-jin, and toward In-ho. Viewers complained about the lopsided screen time, Park asked the production in public why his scenes were not airing, and Soonkki said the producers had stopped consulting her. Seo played what he was handed. He still became a star at the exact moment the show’s own audience was debating whether he deserved the minutes.

His first lead was almost too tidy a joke. In tvN’s Korean remake of Entourage he played Cha Young-bin, a rising star known mostly for his looks, with artistic ambitions his talent had not yet earned. The series averaged roughly 1% of the national audience and sank to 0.6%. Its failure owed more to an American format that never settled into Korean prime time than to its lead, yet the casting said plenty about how the industry saw him then. The handsome one, hired to play the handsome one.

The next stretch reads like an attempt to escape that box from the inside. In KBS2’s Are You Human? he played both a chaebol heir lying in a coma and the android built to stand in for him, a double role about replaceability years before he said the word on stage; it earned him an excellence award and a best-couple prize with Gong Seung-yeon at the KBS Drama Awards. The Third Charm, opposite Esom, and When the Weather Is Fine, opposite Park Min-young, kept him in the romantic lane. The outlier was Watcher, OCN’s thriller about police internal affairs, where he played a young officer carrying a family tragedy, across from Han Suk-kyu. He called it the hardest job he had taken, and told Elle that the more he acted, the more of his own shortcomings he could see.

The Disney+ thriller Grid, with Kim Ah-joong and Kim Moo-yul, reached screens in February 2022, three months after he had enlisted. He served 18 months of active duty and was discharged in May 2023. For Korean actors of his age that gap works like a trapdoor. Audiences move on, a younger face takes the slot, and the comeback project has to explain why the old one still matters.

Undercover High School was his explanation. MBC cast him as Jeong Hae-seong, a demoted agent of the National Intelligence Service sent back to a high school, disguised as a student, to trace gold bars that once belonged to Emperor Gojong. The comedy depended on a man past thirty trying to pass for a teenager, played straight enough that the fights still landed. The show peaked at 8.3% nationwide with its fourth episode and finished as MBC’s most-watched Friday-Saturday drama of 2025. On 30 December it was named Drama of the Year, and Seo took the Daesang, the first of his career.

What the trophy was worth is being tested in public right now. In March 2026 he appeared as a guest in Netflix‘s Boyfriend on Demand, playing a kumdo athlete who exists only inside the virtual-dating service at the centre of the Jisoo and Seo In-guk comedy. On 12 September he opened KBS2’s A Love Other Than Yours with Ahn Eun-jin, playing Namgoong Ho, a confectionery-company manager ten years into a relationship with a film director who is no longer sure she wants to marry him. It is a quiet, adult part with none of the disguise comedy that won him the prize. The audience has been slow to follow: 2.6% for the premiere and 2.1% for the fifth episode, and Korean entertainment outlets were already writing about the drama’s lowest marks by its third episode.

Weekend ratings on a public broadcaster are a blunt measure, and nine of the fourteen episodes have yet to air. Choosing a small, uneasy love story straight after a broad action comedy is the move of an actor who has stopped defending his face and started guarding his range. The rest of A Love Other Than Yours will show whether viewers are willing to follow him somewhere quieter.