Defeated by A.I., a Legend in the Board Game Go Warns: Get Ready for What’s Next

Lee Saedol was the finest Go player of his generation when he suffered a decisive loss, defeated not by a human opponent but by artificial intelligence.

Mr. Lee was beaten by AlphaGo, an A.I. computer program developed by Google’s DeepMind unit. The stunning upset, in 2016, made headlines around the world and looked like a clear sign that artificial intelligence was entering a new, profoundly unsettling era.

By besting Mr. Lee, an 18-time world champion revered for his intuitive and creative style of play, AlphaGo had solved one of computer science’s greatest challenges: teaching itself the abstract strategy needed to win at Go, widely considered the world’s most complex board game.

“I am very surprised because I have never thought I would lose,” Mr. Lee said at the time in a post-match news conference. “I didn’t know that AlphaGo would play such a perfect Go.”