He was the chairman and CEO of NXC Corporation, the holding company of Nexon, and a partner at Collaborative Fund, a New York-based venture capital firm.

[5] Under Kim's leadership, Nexon launched the world's first graphic massively multiplayer online role-playing game (MMORPG), Nexus: The Kingdom of the Winds and released popular titles such as MapleStory, KartRider, Mabinogi and Dungeon&Fighter.

[6][7] With offices in Korea, Japan, United States, Europe and Taiwan, Nexon services over 100 online and mobile games to over 190 countries.

[18] In 2019, according to media reports, it was announced that Kim was preparing to sell his controlling stake in NXC Corp for an estimated $9 billion (USD).

[29] In October 2020, the foundation announced its donation of ₩10 billion (US$8,500,000)[30] to Seoul National University Hospital (SNUH) to fund the establishment of the Nexon Children's Palliative Care Center, which is set to open in 2022.

[32] In partnership with Nexon Foundation, Kim founded SOHO Impact, a US-based non-profit organization promoting creativity in kids through brick play programs.

[33] He was also a founding board member of C-Program, a venture philanthropy fund jointly established by the founders of Nexon, Naver, Kakao, Daum and NCSoft.

[34] Kim was a key figure behind Korea's first-generation tech wave, launching Nexon in 1994 as a game-developing startup and pioneering the freemium gaming business model.

[35] In 2012, he received the Presidential Award, Tin Tower Order of Industrial Service Merit for his contributions as a distinguished entrepreneur in South Korea.

[42] According to Nexon holding company NXC, which announced Kim's death on 1 March,[40] he had been receiving treatment for depression, which "seemed to have worsened recently".