world champion has retired because he has decided humans cannot beat computers at his game. grand champion is Lee Se-Dol from South Korea. He was world champion at ancient, strategy board game Go. Some people compare Go to chess. Mr Lee is only person in world to ever beat Google's AlphaGo computer algorithm. This is special A.I. computer program created by Google to play Go. Mr Lee, 18-time world champion, told reporters earlier this week that: "Even if I become number one, there is entity that cannot be defeated. With debut of A.I. in Go games, I've realized that I'm not at the top even if I become the number one."
game of Go originated in China around 3,000 years ago. Today, it is played mostly in China, Japan and South Korea. It is believed to be oldest board game in world. In 2016, International Go Federation said it had 75 member nations, and that over 46 million people worldwide knew how to play Go. Mr Lee started playing at age of five. He turned professional seven years later, when he was 12. He played five games against Google's AlphaGo and lost four of them. He said his one victory was because of "bug" in program. The bug did not know what to do when Mr Lee made "tricky" move. Today's Go programs are much more powerful than one that beat Mr Lee.