Kim Yoon-sung (; born January 14, 1981), known professionally as Gaeko () is a South Korean hip hop recording artist. He and Choiza comprise the hip hop duo Dynamic Duo, which rose to fame upon the release of their debut album Taxi Driver in 2004. In 2015, he released his first solo album, Redingray.
On May 14, 2011, in the middle of his mandatory military service, he married Kim Su-mi before returning to serve the rest of his term. The couple had a son, Tae-woo, in 2011 and a daughter, Seo-ah, in 2015.