Lee Sedol (Korean: ???; 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").
He was defeated by the computer program AlphaGo in a 1–4 series in March 2016.On 19 November 2019, Lee announced his retirement from professional play, arguing that he could never be the top overall player of Go due to the increasing dominance of AI.
Lee referred to them as being "an entity that cannot be defeated".