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).