Launched to fame as the young girl abducted by a sea monster in box-office smash "The Host" (2006), Ko Ah-sung made the transition from child actor to adult thespian appear effortless with acclaimed performances in indie romance "Duet" (2012), sci-fi thriller "Snowpiercer" (2013) and emotional drama "Elegant Lies" (2014). Born in Seoul, South Korea in 1992, Ko appeared in various TV commercials from the age of four and made her acting debut in a musical theater production of "Peter Pan" before venturing onto the small screen in children's series "Oolla Boolla Blue-jjang" (KBS 2004). Following small parts in big-budget melodrama "Sad Love Story" (MBC 2005) and miniseries "Beating Heart" (MBC 2005), Ko went through an extensive audition process to land the role of Park Hyun-seo, the young girl kidnapped by an amphibious creature in Bong Joon-ho's globally successful monster movie "The Host" (2006). Ko then built on her new-found high profile with performances in rock n' roll reunion film "The Happy Life" (2007) and the comedic tale of Korea's first radio station, "Radio Dayz" (2008), and gained further acclaim for her portrayal of amputee Ye-shin in Ounie Lecomte's semi-autobiographical directorial debut "A Brand New Life" (2009). After appearing as a surprise wedding guest in feature-length mini drama "After The Banquet" (2009), Ko returned to television as hard-working student Gil Pul-ip in "Master Of Study" (KBS2 2010), the teen drama based on Japanese comic series Dragon Zakura. In indie romance "Duet" (2012), she showcased her impressive vocal skills as an aspiring Korean singer who falls in love with a British man, while a year later, she reunited with Joon-ho for her first foray into English-language cinema where she played the drug-addicted psychic Yona in the dystopian sci-fi thriller "Snowpiercer" (2013). Ko was then cast as Man-ji, a grief-stricken girl who attempts to seek the truth about her sister's suicide, in the adaptation of Kim Ryeo-ryeong's novel "Elegant Lies" (2014).