[4] Before making his debut as a voice actor, he used to work in theaters, including performing his roles as a Japanese assassinator and a royal servant in a 1997 South Korean musical The Last Empress[5] and working as the assistant director for South Korean musicals Gaeddongi[6] and Moskito[7] the same year.

In the early 2000s, he came to prominence after voicing Kira Yamato on the Korean dub of Mobile Suit Gundam SEED.

Since then, Um has dubbed a number of television animation series such as Chrono Crusade, Digimon Frontier, Fullmetal Alchemist, InuYasha and School Rumble.

He became the recipient of the award for his role as Po in Kung Fu Panda: Legends of Awesomeness, gaining 3,121 votes, which is about 38% of the entire poll.

[9] Although having been highly active as a freelancer for more than a decade, Um is also still one of the main voice actors representing EBS.