Daniel Ko (고단열) is an alto saxophonist who was born in Seoul, grew up in Ottawa, trained at Berklee in Boston and has worked in Seoul since 2016. He leads a trio that made the album Sleepless in Seoul (2018), plays in the drummer Soojin Suh's Chordless Quartet and records free improvisation with her as a duo. His birth date is not published. Berklee and the Seoul daily Newstomato both call him a Canadian saxophonist, and no source states his citizenship; his working life since 2016 is in Korea, where he is billed in Hangul as 고단열.

The most detailed account of his early life is the biography for the 2018 Hermann's Jazz Club concert in Victoria, British Columbia. It says he began music in church, starting piano at the age of three, and moved to Canada a short time later, where American music led him to the saxophone. His mouthpiece sponsor's biography places that start in Ottawa and says he began jazz saxophone at an early age. Berklee's own video profile follows the same arc, from middle-school big band to Charlie Parker to the college, and it names him a Slaight Scholar. The Hermann's biography dates the Slaight scholarship to 2011, and his mouthpiece biography describes it as awarded to one Canadian a year and covering full tuition.

In Boston he played with local musicians including the trumpeters Jason Palmer and Ingrid Jensen and the saxophonist Godwin Louis, according to his mouthpiece biography; the Hermann's biography adds the drummers Ralph Peterson and Neal Smith and the bassist Ray Drummond. A 2015 Berklee compilation, Transitions (Jazz Revelation Records), lists him as a featured player on the track "One For Ct". Earlier and later credits from Ottawa appear under the same Discogs entry: alto saxophone on three tracks of the singer-songwriter Jeff Rogers's album Let It Show (2012) and on the Tariq Amery Group's debut Indefinity (2017), recorded at Gallery Studios in Ottawa. His mouthpiece biography says that after graduation he played clubs and festivals including the Blue Note, Smalls Jazz Club, The Rex in Toronto and the Ottawa International Jazz Festival.

He returned to Korea in 2016 and took up the Seoul scene quickly. On August 25, 2017, at the final of the first Yongin Jazz Festival competition at the Yongin Poeun Art Hall, he took the top prize in the general division with a solo saxophone performance of "Skylark", as the newspaper Joongboo Ilbo reported two days later; it also reported his thanks for a competition that gives jazz players a chance to be heard. A September 2017 preview of a Gyeongnam jazz concert series listed him among the friends the drummer Minchan Kim brought together for a modern-jazz program, with the trumpeter Hong Tae-hun and the bassist Kim Dae-ho. On December 30 and 31, 2017, he played saxophone in the band behind the singer Lee Juck (이적) at the concert 멋진 겨울날 at COEX in Seoul, according to a review in Bridge Economy. His mouthpiece biography also says he recorded on an album by Lee Juck, without naming it, and that Jazz People magazine named him a Rising Star in 2018.

The year 2018 was his busiest on record. In April the Chordless Quartet of Soojin Suh released Strange Liberation (Mirrorball Music), with Ko on alto saxophone, Sunjae Lee on tenor and soprano saxophones and Hoo Kim on double bass; the band takes its name from a rule of leaving out piano and guitar. On June 21 his own album Sleepless in Seoul appeared digitally, six pieces by a trio with the bassist Sean Drabitt and the drummer Minchan Kim, and on June 28 the same trio played Hermann's Jazz Club in Victoria as part of a festival night billed "From Korea". The tracks are "Line for Lyons", "I Want to Be Happy", "Smoke Gets in Your Eyes", "Billy Boy", "Flashback" and the title piece; his mouthpiece biography calls it an album of standards and originals that drew critical acclaim.

In 2019 he was billed for a concert in Ulsan on October 19 as one of the soloists with the vocalist Heo So-young (허소영), alongside the double bassist Shin Dong-ha, Minchan Kim and the pianist Kwak Jeong-min. On November 20, 2019, he was billed in the Chordless Quartet at Akbank Sanat in Istanbul, with Hachul Song on soprano and tenor saxophones, Younghoo Kim on bass and Suh on drums.

The autumn of 2020 shows both sides of his playing. On October 18 he and the alto saxophonist Nam Yu-sun (남유선) were to take the two halves of Charlie Parker@100, a concert at Pomtech Works Hall in Seoul marking the centenary of Charlie Parker: Ko was to play the faithful half, with Sim Gyu-min on piano, Sean Drabitt on bass and Kim Min-chan on drums, while Nam reworked the music with electronics. Newstomato's Kwon Ik-do met them beforehand. Ko said he had been studying decades-old bootleg recordings of Parker and a 1954 interview with Paul Desmond, that he loved Parker's frankness about playing the only way he could, and that he wanted to get as close to the New York sound as he could. Earlier that month, on October 7, he and Suh had taped Alchemy, a nine-track duo of tenor and alto saxophones, with a bamboo flute on the last piece, and drums, recorded on a Tascam 424 cassette machine in Seoul and released in November on Mung Music; Sunjae Lee recorded, mixed, mastered and designed it. The label's notes call the two longtime collaborators and say the album turns from their usual conventional jazz settings to free improvisation. For November 14 he was billed with the bassist Sean Drabitt, Minchan Kim and the pianist Paul Kirby at the chamber group We Soloists' 22nd regular concert, "Just Friends", in the IBK Chamber Hall of the Seoul Arts Center, a program of jazz arrangements of music by Bach, Mozart, Bernstein and Gershwin.

His last listed recording is the Chordless Quartet's Roots to Branches (April 2021), again with Suh, Hoo Kim and Sunjae Lee. No later album under his own name is listed; his YouTube channel describes him as a musician, composer and saxophonist who takes gigs, lessons and recording work in Korea.

The biographies place him in the bebop alto tradition, with a grounding in bebop, an energetic improvising style and a sound that mixes the jazz tradition with the contemporary scene and the local Korean one. His own words about Parker point the same way: he has described studying Parker's recordings and spoken interviews to reproduce the sound as closely as he can, and he sees jazz as a music in which players trade ideas across eras. The standards on Sleepless in Seoul, among them "I Want to Be Happy" and "Smoke Gets in Your Eyes", sit beside an original title piece.

The other half of his work is free improvisation. Alchemy, the duo with Suh, and the Chordless Quartet's two albums are filed on Discogs under Free Jazz and Free Improvisation. The Chordless Quartet's concept, as Suh's liner text puts it, is freedom without chordal instruments, a freedom that takes others into account. Where Alchemy borrows folk and religious melodies, as its label puts it, they serve as starting points before long solos in the manner of late-1960s saxophone and drum duos.