Yeon's first feature-length animation was "The King of Pigs" (2011), about a man who kills his wife after his business goes bankrupt, and seeks out his long-lost friend, a ghostwriter, 15 years after both had been severely bullied as adolescents in middle school. Inspired by the works of Satoshi Kon and Minoru Furuya, Yeon said the incidents in the film were drawn from his own life, and he cried while writing the screenplay. The low-budget () film drew widespread critical acclaim for its raw portrayal of bullying, violence and systemic poverty (and the lifelong effects of such oppression), as well as the psychology of public attitudes toward a hero figure. It became the first Korean animated film to be invited to the Cannes Film Festival, where it screened in the 2012 Directors' Fortnight sidebar. It won numerous awards at domestic and international film festivals, including the Director's Guild of Korea Award for Best Director, CGV Movie Collage Award, and NETPAC Award at the 2011 Busan International Film Festival, the Satoshi Kon Award for Achievement in Animation and Special Mention (New Flesh Award for Best First Feature) at the 2012 Fantasia International Film Festival, and the Jury Prize at the 2013 Jameson Dublin International Film Festival.