Seo In-guk came from a family in Ulsan. He started dreaming of becoming a singer at the age of 10, after listening to Korean rocker Kim Jung-min. The young Seo discovered his talent by standing on stage at family gatherings and school events. He studied Applied Music at Daebul University, and eventually started to audition at entertainment agencies. After being repeatedly rejected and told to lose weight, Seo struggled withbulimia, but fortunately, the vomiting only damaged his vocal cords temporarily.
Despite the setbacks, in 2009 he joined Mnet’s talent reality show Superstar K. He won that first season of the show.
The subsequent spotlight came with a hectic schedule of recordings, photo shoots, interviews and television broadcasts, followed by chart-topping singles and albums. Seo also had to deal with the negative consequences of fame, including plastic surgery rumors, and cold-shoulder treatment from the three major networks for cable stars like him.
In 2012 Seo became part of the cast of homegrown jukebox musicalGwanghwamun Love Song. He then made his onscreen acting debut with a supporting role in KBS’s Love Rain. Aiming to expand his career in Japan, he also signed with Japanese agency Irving Entertainment.
He landed his first leading role later that year, in cable channel tvN’s ‘90s nostalgic hit drama Reply 1997. Seo’s portrayal of a teenage boy in unrequited love with his childhood best friend won praise from both audiences and critics. He also recorded two singles for the soundtrack (both duets with costar Jung Eun-ji), and one of them,“All For You”, became one of the best-selling singles of the year on the Gaon Single Chart.
Shortly after, he appeared in MBC’s The Sons (also known as Rascal Sons), saying he chose the 50-episode weekend family drama because he wanted to watch and learn from his senior colleagues in the ensemble cast.
Seo joined the newly launched reality/variety show I Live Alone from January to June of 2013. He was also cast in the romantic comedy film Police Family, about a girl from a family of policemen who marries a young man from a family of criminals.
Seo returned to the music scene in April 2013 with the single With Laughter or with Tears. The title song is the first time he sang a soulful ballad. Actress Ku Hye-sun appeared in the music video, which depicts the agony after a break up. This was followed several weeks later by his Japanese debut, with the release of the single Fly Away.
In June 2013, he was cast in Master’s Sun, a horror-romantic comedy TV series written by the Hong Sisters, playing a former soldier who served in the Zaytun Division and who, after his discharge, becomes the head of security for a shopping mall company.
He then played a dual role in Another Parting, a five-episode miniseries about a man and a woman who meet in the final moment of their lives and spend one special day together. Produced by LOEN Entertainment, the drama premiered on February 17, 2014 onTaekwang Group-owned cable channel Dramacube (also airing on BTV and YouTube).
Wanting to try a different genre, Seo was cast as a young gangster in the 2014 action-noir film Wild Dog, but like Police Family, it ran into investor troubles and was unable to begin production (Police Family was later released as Enemies In-Law, with Hong Jong-hyun as lead actor). Instead, Seo headlined another cable romantic comedy series, High School King of Savvy, in which he played a high school student and star hockey player who leads a double life when he’s forced to take on his older brother’s job as an executive at an IT company. Later that year, Seo starred in his first period dramaThe King’s Face, playing illegitimate crown prince Gwanghae, who becomes his father King Seonjo’s rival in politics and love.