Ahn Yeon-seok (born April 11, 1984), better known by the stage name Yoo Yeon-seok, is a South Korean actor. After making his acting debut in 2003 with a small role in Oldboy, he resumed his acting career in 2008. His notable works include the films Re-encounter (2011), Architecture 101 (2012), A Werewolf Boy (2012), Whistle Blower (2014), and Love, Lies (2016), as well as the television series Reply 1994 (2013), Dr. Romantic (2016), Mr. Sunshine (2018), Hospital Playlist (2020-2021), and When the Phone Rings (2024).