Lee Sedol

• 1. Introduction

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  Lee Sedol grew up on Bigeumdo Island, a small island off the coast of South Korea, and by the age of 12 years and 4 months he had already become a professional Go player. That made him the fifth-youngest professional in South Korean history. Nobody on that island could have predicted that three decades later, his name would be everywhere, not because of a title he won, but because of a match he lost.

  In March 2016, Lee sat down across from a computer program called AlphaGo and played five games in front of a watching world. He went in supremely confident. He came out with one win, four losses, and a quiet sense that the game he had dedicated his life to had shifted beneath him in a way that could not be undone. What follows is the story of how a boy from Bigeumdo became the second-ranked player in international titles, pulled off one of the most celebrated single moves in the history of Go, and then walked away from the board entirely because of something a machine did to him.

• 2. The Strong Stone

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  Lee's nickname, "The Strong Stone," or "Ssen-dol" in Korean, is not just a translation of his name. It describes a style of play that made him one of the most decorated Go players of his generation. He turned professional on the 2nd of July 1995 as a 1 dan, and by the 7th of July 2003 he had reached the pinnacle of 9 dan rank.

  His climb was unusually rapid. On the 28th of March 2003, he won the 7th LG Cup against Lee Chang-ho, and the Hanguk Kiwon promotion rules allowed him to skip the 4 dan and 5 dan ranks entirely, going straight to 6 dan. By July of that year, after winning the 16th Fujitsu Cup against Song Taekon, he leapt again, this time past 8 dan, arriving at the top rank in a single bound.

  By February 2016, Lee held 18 international titles, placing him second globally behind only Lee Chang-ho, who held 21. He also ranked third in total domestic titles across Korea. Despite this record, he described his opening play, the first critical moments of any game, as "very weak." That admission is the kind of thing only a player of extraordinary depth can say honestly, because his record in the middle and late stages of games told an entirely different story.

• 3. The Broken Ladder

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  On the 23rd of April 2003, in a game played during the KAT Cup against Hong Chang-sik, Lee Sedol did something that beginners are specifically told never to do. He used a broken ladder formation.

  A broken ladder is a sequence in Go where a player tries to chase an opponent's stone in a zigzagging pattern across the board. Among experts, playing one out is considered almost automatically decisive in the opponent's favor, because the chasing stones are left scattered and weak. It is the kind of move that signals a player who does not understand the game.

  Playing as black, Lee reversed that logic. He used the broken ladder to capture a large group of Hong Chang-sik's stones on the lower-right side of the board. Corner stones that had previously been written off as dead came back to life. Hong ultimately resigned. The game ran to move 211 before that resignation, with the critical sequence running from move 67 through move 97. That game became a landmark example of creative play within a tradition built on accumulated wisdom about what is and is not possible on the board.

• 4. Five Games Against AlphaGo

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  Before the match against AlphaGo began on the 9th of March 2016, Lee told Yonhap News that he was confident of winning by a score of 5-0, or at least 4-1. When asked about the program's improvements over the previous months, he said, "Of course, there would have been many updates in the last four or five months, but that isn't enough time to challenge me."

  AlphaGo was developed by Google DeepMind, a London-based artificial intelligence firm. The match prize was $1 million. The series was broadcast live. In an earlier interview on the 22nd of February 2016 with Sohn Suk-hee of JTBC Newsroom, Lee had shown confidence while also raising a curious concern: that even winning 4-1 might allow Google DeepMind to claim a kind of moral victory, framing the one loss as a defeat of humanity. He also noted that the time rules for the match seemed well-balanced, such that both sides would face equal time pressure.

  Lee lost the first game on the 9th of March by resignation, playing as black. He lost the second on the 10th of March, playing white. He lost the third on the 12th of March, again as black. Then came the 13th of March.

  Playing as white in Game 4, Lee made a move at White 78 that observers described as "a brilliant tesuji." Gu Li, a 9 dan professional, called it "a divine move" and said it had been completely unforeseen by him. The commentary platform GoGameGuru wrote that the game would "almost certainly become a famous game in the history of Go." Lee won.

  Afterward, Lee said: "I don't think I've ever felt so good after winning just one game." He added: "I, Lee Se-dol, lost, but mankind did not."

  For the fifth and final game on the 15th of March, Lee requested to play black. He believed AlphaGo was strongest playing white, and he thought winning with black a second time would carry more weight than another white win. He also noted that black is considered more risky under Chinese Go rules. He lost. The final series score was 1-4.

• 5. Retirement and What Followed

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  On the 19th of November 2019, Lee Sedol announced his retirement from professional Go. His stated reason was straightforward: "Even if I become the number one, there is an entity that cannot be defeated."

  In December of that same year, he played a three-game match against HanDol, an AI system developed by Korean NHN Entertainment Corporation. Lee received a two-stone handicap in the first and third games. He won the first game. HanDol won the next two. The final score was 2-1 in the AI's favor.

  In a 2024 interview, Lee reflected on what the AlphaGo loss had cost him: "Losing to AI, in a sense, meant my entire world was collapsing. I could no longer enjoy the game. So I retired." That statement carries unusual weight. His career record through 2019 showed 980 wins against 437 losses, a total win rate of 69.2 percent across more than two decades of professional competition. In his peak year of 2010, he won 74 games against only 14 losses, a win rate of 84.1 percent. A player who had mastered the game at that level found the game itself altered by something outside the tradition entirely. By February 2013, years before AlphaGo, he had already told the press he planned to retire and move to the United States to promote Go. The plan that arrived was different from any he had imagined.