Short answers, pulled from the story.
Lee Sedol is a South Korean former professional Go player of 9 dan rank, born on the 2nd of March 1983. He held 18 international titles as of February 2016, placing him second globally behind Lee Chang-ho. He is widely known for playing a five-game match against the AI program AlphaGo in March 2016, which he lost 1-4.
Lee Sedol became a professional Go player at the age of 12 years and 4 months, making him the fifth-youngest professional in South Korean history. He turned pro on the 2nd of July 1995 as a 1 dan.
Lee Sedol played a five-game match against AlphaGo, developed by Google DeepMind, starting on the 9th of March 2016, for a $1 million prize. He lost four games and won one, for a final score of 1-4. His single win in Game 4 came from a move at White 78 that commentators called a "divine move."
Lee Sedol announced his retirement on the 19th of November 2019, saying "Even if I become the number one, there is an entity that cannot be defeated." In a 2024 interview he elaborated that losing to AI meant his entire world was collapsing and he could no longer enjoy the game.
On the 23rd of April 2003, during the KAT Cup against Hong Chang-sik, Lee Sedol used a broken ladder formation, a sequence normally considered a beginner's mistake among expert players. Playing as black, he used it to capture a large group of Hong's stones and revive previously dead corner stones, forcing Hong to resign at move 211.
Lee Sedol finished his professional career with 980 wins and 437 losses, for a total win rate of 69.2 percent. His strongest single season was 2010, when he went 74-14 for an 84.1 percent win rate. He held 18 international titles and ranked third in total domestic titles in Korea.