Lee Young Soo, known professionally as Mill, is a South Korean singer, dancer, actor, and member of ONLYONEOF (온리원오브). He graduated from Jakjeon High School.

He made his debut in May 2019 as the group's main rapper and vocalist with their first mini-album, "Dot Point Jump". Their agency, 8D Entertainment (에잇디엔터테인먼트), wanted them to have the concept of being "ubersexual" (meaning mixing sexiness and masculinity with a hint of softness). They trained for three years, coming up with songs, stage compositions, costumes and concepts themselves for the weekly evaluations. Billboard named them one of the K-pop rookie groups to watch in 2020.

In April 2021, they faced some controversy when they released the single "Libido", part of their third mini album "Instinct Part. 1". KB and Nine were in charge of composing the song, and it dealt with sexual instinct and desires, something rarely explored for a South Korean idol group. The choreography was deemed too suggestive by some music critics as the members touched each other's bodies and used strings. However, the song was chosen as the best Korean music video of 2021 by Rolling Stone India for breaking boundaries and representing the LGBTQ+ community.

In November 2022, he made his debut as a solo artist with the single "Beat". Then, in November 2023, the whole group was cast in the BL drama "Bump Up Business". They spent most of 2024 on an international tour.

In October 2025, 8D Entertainment announced that ONLYONEOF's contracts had expired and that they would no longer be managing them, which led to confusion around the group's status, with people speculating that the group had disbanded. However, he confirmed that they have not disbanded and encouraged fans to continue looking forward to their future activities.

(Source: MyDramaList) Edit Biography