Jean Oh (오정수) is a Seoul-born guitarist, composer and producer who works in three overlapping worlds: modern jazz guitar, free improvisation, and the Korean-instrument fusion of the quartet Black String, where he plays guitar and electronics. Korean press and many credits print his name as Oh Jeong-su, while his own records, Apple Music and Discogs use Jean Oh. His All About Jazz biography gives his birth date as June 11, 1978, in Seoul, which makes him 48. He has put his own name on albums since 2008, and since 2016 he has been the guitarist on Black String's records for the German label ACT.

According to that biography he began playing guitar at 13 and studied formally at the Seoul Jazz Academy, then played in bands around Seoul for several years before deciding he needed different experience. That took him to Paris, where he names Misja Fitzgerald Michel, Sylvain Beuf, Bernard Maury, Joe Malcolm, Emil Spanyi and Frederic Favarel among his jazz teachers, played in clubs and graduated from a conservatory; the label text for his debut album names it as the conservatory of the Vallee de Chevreuse. From there he went to New York University, where over two years he earned a master's degree and, by his account, studied with Ralph Alessi, George Garzone, John Scofield and Gil Goldstein. The same biography adds study at the School of Improvisation Music, as it calls it, with Steve Coleman, Mark Helias, Uri Caine and David Binney, and says he has toured the United States, Canada, Japan, South America, the Philippines and Russia. These teachers are named in his own biography; no other source for the lessons was found.

His first album as a leader, Invisible Worth, came out in 2008 on WIT Records. Apple Music dates it September 19, 2008 and Bugs lists a November 6 release in Korea; the label text presents it as a simultaneous Korean and American release made while he was working in New York. It has eleven tracks and about 58 minutes of music, with Garzone on tenor saxophone, John Lockwood on bass and Jeff Hirshfield on drums. Among the tracks are "Blues for Calvin," one titled "Piece for Dennis Erwin," the title piece and a reading of the standard "It Never Entered My Mind."

Back in Seoul he became part of the circle around the Mirrorball and Audioguy labels. He was one of six musicians in the Lee Pan-geun Project, which re-arranged songs by the jazz composer and theorist Lee Pan-geun for the album A Rhapsody in Cold Age (Leeway Music & Media, October 10, 2010) and won the Best Jazz & Crossover Performance prize at the Korean Music Awards in February 2011, according to the Indieful ROK report on that year's winners. On July 18, 2011 Sony Music released Is This All the Love You Have?, a collaboration with the pianist Jangeun Bae (배장은) built from the two players' own compositions, with the bassist Wonsool Lee and a fourth player, Sean Pickler, joining for three improvised pieces. The label text for the record quotes Garzone calling Oh a new guitarist who deserves wide attention. The duo was a nominee for Best Jazz & Crossover Jazz Album at the 9th Korean Music Awards on February 29, 2012, the night the prize went to BG Salon, according to Edaily.

The year 2012 shows how widely he was working. In February he was one of two guitarists, with Hyuck Bang (방혁), in the live quartet recording Reverberation led by the bassist Kim Changhyun, with the drummer Kim Chaek (김책). In January he recorded a trio album with Wonsool Lee on bass and the drummer Lee Do-heon (이도헌), mixed and mastered at Avatar Studio in New York, which Kimbap Records released on January 17, 2014 as 어제가 있는 자화상 (roughly, a self-portrait with a yesterday). It holds three originals by Oh, group pieces such as "Egon Schiele" and "Brainstorm," the standard "My Foolish Heart," Ornette Coleman's "Round Trip," Ha Duk-kyu's "가시나무" and the children's song "섬집아기." In October 2012 Audioguy released '나'의 발견 (roughly, Discovery of the Self), a duo with the drummer Check Kim (김책, billed Kim Chaek elsewhere) that the release text says was made in half a day of improvisation with no ideas decided beforehand; Bugs files it as free jazz. It was one of five nominees for Best Jazz & Crossover Performance at the 10th Korean Music Awards (nominees announced January 29, 2013), alongside Kim Changhyun's Reverberation; the saxophonist Kang Tae-hwan's Sorefa won. In October 2014 Mirrorball Music issued A Lonely Sight, a trio record in which Oh, Wonsool Lee and the Icelandic trumpeter and flugelhorn player Birkir Matthiasson each brought three pieces.

He also led and co-led bands outside the jazz-club circuit. Gosaek Changyeon (고색창연) is a quartet of Hyuck Bang and Oh on guitars, Seo Yeong-do (서영도) on bass and Seo Hyeon-jeong (서현정) on drums, formed to take a different Korean popular songwriter in each album; its first, 하나, 외로운 사람들, a set of songs by Lee Jung-sun, came out on Mirrorball Music on February 24, 2015, and its release text calls it Oh's eighth album as a leader or co-leader.

Black String is the part of his work heard farthest from Seoul. The quartet, formed in 2011 around the geomungo player Heo Yoon-jeong, recorded Mask Dance in Seoul in June 2016 for ACT, followed by Karma in 2019, took part in the live album Jazz at Berlin Philharmonic X - East-West in 2020, and released Road of Oasis in December 2024; Discogs files his three ACT credits under his name. The band's own profile on JazzProfiles.com covers its awards and tours. In January 2024 he and Aram Lee, the group's daegeum player, were in residency at CultureHub in Los Angeles, with a free concert in Los Angeles on January 15 and an improvised music and dance event with California Institute of the Arts faculty on January 16. CultureHub describes the two of them as co-directors of the music program at the Seoul Institute of the Arts.

Under the name Yohrn (욘) he also makes electronic and indie songs on which he plays every instrument and sings. The singles "미지의 세계" (October 26, 2023) and "타인의 죽음" (November 2, 2023) led to the six-track EP Murmur of Earth (Mirrorball Music, November 16, 2023), produced with the photographer Seung-yull Nah and Black String's own executive producer Myung-guk Kye as executive producers. His other recent credits include guitar on Nam Yeji's 2024 album Old Songs, Tmmm, produced by Wonsool Lee; electronics and arrangement on two 2025 singles by the singer-songwriter Jisun Seong (성지선); and production of the Kitty Moon EP Koreander Smash, released on June 12, 2026.

The thing people keep describing is his tone. The release text for the 2011 duo album says Jazz Inside Magazine in New York praised the beauty within the plainness of his tone, and quotes the critic Kim Hyeon-jun finding him more precise and meticulous than anyone else on the scene. The text for his 2014 trio album names Kim and Garzone among the players and critics who talk about his tone, and compares a guitarist's tone to a singer's voice. As a jazz guitarist he plays standards and Ornette Coleman alongside his own writing, and his duo with Check Kim goes as far toward open improvisation as a record can. In Black String his electric guitar and electronics bring rock and electronic color into a band otherwise made of Korean traditional instruments.

Whether he counts as primarily a jazz musician is a fair question. For jazz: he trained in Paris and New York with jazz teachers, plays on albums filed under jazz by Bugs and Apple Music, recorded with Garzone, belonged to a Korean Music Awards winner in the Jazz & Crossover field and to a nominated duo, and his collaborators (Wonsool Lee, Jangeun Bae, Birkir Matthiasson, Kim Changhyun) are jazz players. Against: the project that carries his name abroad, Black String, sits between jazz and Korean traditional music, and its leader has said she thinks of the music as free music beyond genre; his Yohrn songs are electronic and indie pop; he also produces indie rock for other artists; and CultureHub describes him as a guitarist, composer, producer, DJ and educator working across jazz, world music and indie pop. This profile treats him as a jazz guitarist whose work reaches into Korean-instrument fusion and electronics.