Seo In-guk (born October 23, 1987) is a South Korean singer-songwriter and actor. He began his singing career after winning the talent reality show Superstar K in 2009, and made his acting breakthrough in Reply 1997 (2012). Since then, he has starred in television series, High School King of Savvy (2014), Hello Monster (2015), Shopping King Louie (2016), and Death's Game (2023).