Yoo Jae-Seok (Hangul: 유재석; or spelled Yu Jae-Suk; born on August 14, 1972) is a South Korean comedian and television comedy show host. Nicknamed as "MC of the nation" (국민 MC), people (netizens) have voted him for the most popular Korean comedian for five consecutive years (since 2004). He has hosted several variety television shows in South Korea, including the hugely popular program Infinite Challenge. Nicknamed "The Grasshopper", due to early appearances dressed as a grasshopper, he is now known for his quick wit and likability with most demographics, and has established himself as one of Korea's top comedians and TV personalities.

Yoo Jae-Suk was born as the first child out of three (he has two younger sisters) on August 14, 1972 in Seoul, South Korea. Yoo Jae-Suk attended the Seoul Institute of the Arts, but had been unable to receive his degree due to his busy schedule as a comedian.

His television debut was on the KBS Comedian Festival (for college students) in 1991, performing a parody of a commercial with Choi Seung-Gyung (Hangul: 최승경). In Infinity Challenge, him dancing to a cover of the song "Step by Step" by New Kids on the Block was shown as one of his early memorable moments. After nine years of hard times, in 2000, he hosted a program called Live and Enjoy Together (Dong-guh-dong-lak), thanks to Choi Jin-Sil's recommendation. The program became instantly popular, and since then, Yoo began to host many other variety programs. His potentiality was fully shown when he co-hosted a program called The Crash of MCs (MC 대격돌 – 공포의 쿵쿵따) with Kang Ho-Dong, Lee Hui-Jae and Kim Han-Seok.