Lee Sedol (; born 2 March 1983), or Lee Se-dol, is a former South Korean professional Go player of 9 dan rank. As of February 2016, he ranked second in international titles (18), behind only Lee Chang-ho (21). He is the fifth youngest (12 years 4 months) to become a professional Go player in South Korean history behind Cho Hun-hyun (9 years 7 months), Lee Chang-ho (11 years 1 months), Cho Hye-yeon (11 years 10 months) and Choi Cheol-han (12 years 2 months). His nickname is "The Strong Stone" ("Ssen-dol"). In March 2016, he played a notable series of matches against AlphaGo that ended in 1-4.