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