Seo Jung-jin is cofounder of Celltrion, a biopharmaceutical firm that makes drugs to treat cancer, influenza and rheumatoid arthritis, among others. With the success of biosimilars in South Korea, his Celltrion has become a favorite among investors. In March 2021, Seo stepped down as chairman of the Celltrion group. Seo's eldest son Jin-seok now chairs Celltrion Inc. and Celltrion Pharm while his other son Joon-serk chairs Celltrion Healthcare. Seo started Celltrion Inc. in 2002 and took it public in 2008.