Ryu Se Il is a South Korean actor. As a teenager, he was more interested in music than acting and played guitar in a school band, initially imagining a future as a musician. His direction changed after watching One Flew Over the Cuckoo’s Nest, which prompted him to enroll in an acting academy. After repeatedly failing university entrance examinations, he completed his military service and later entered a university musical-theatre department, but withdrew because the programme did not suit him. His practical training instead developed through independent productions and collaborations with theatre artists, including work with students from Korea National University of Arts and appearances at festivals such as the Seoul Fringe Festival.

A decisive part of his career has been his long association with the theatre collective Ballplayclub (공놀이클럽). He met director and playwright Kang Hoon Gu in 2017, collaborated with him on "Boy and Girl Evolution Theory" in 2018, and subsequently became the collective’s principal actor. His most acclaimed work came with "Dried Chilli Peppers and a Peach-Scented Lipstick". The production received the Special Jury Prize at the Seoul Arts Awards, while he and Ballplayclub received the Young Theatre Award at the 61st Baeksang Arts Awards in 2025.

He appeared in his first film in "The Continuing Land", which premiered at the 2022 Seoul Independent Film Festival before receiving a Korean theatrical release in 2024.

His first leading role in a drama followed in 2026 with "Boy, with Caution" (소년, 주의).

(Source: dramabl.com; edited by kisskh) Edit Biography