Uhm Hong-sik (born October 6, 1986), known professionally as Yoo Ah-in, is a South Korean actor, creative director, and gallerist. He is known for playing a diverse spectrum of roles in both television and film, where he often portrays dynamic characters who exhibit significant personal growth. He is the recipient of various accolades including Asian Film Awards, Fantasia International Film Festival's Cheval Noir award, two Blue Dragon Film Awards and two Baeksang Arts Awards. He is best known for his leading roles in coming-of-age film Punch (2011), melodrama Secret Affair (2014), action blockbuster Veteran (2015), period drama The Throne (2015), historical television series Six Flying Dragons (2015-2016), psychological thriller mystery drama Burning (2018), zombie film #Alive (2020), indie crime drama film Voice of Silence (2020), and dark fantasy series Hellbound (2021).

For his role as Lee Jong-su in Burning, Yoo received international critical acclaim, including being selected for The New York Times' "The Best Actors of 2018" feature, making him the only Asian to be on the list and the first Korean actor to do so. Directed by the acclaimed South Korean auteur Lee Chang-dong, the film also received universal acclaim, competing for the Palme d'Or at the 2018 Cannes Film Festival and becoming the first Korean film to make it to the final nine-film shortlist of Best Foreign Language Film at the 91st Academy Awards.In addition to his film work, Yoo engages in social and artistic activism. He is also known for his politically and socially charged views on his social media account. In 2016, he ranked second in Forbes Korea Power Celebrity list.