Google DeepMind's AI has won the fifth and final game of Go against human world champion Lee Sedol.
Lee played as black for the first time in the tournament — possibly to try and confuse the AlphaGo AI — but he still lost.
The victory marks the end of a week-long Challenge Series tournament in South Korea that has caught headlines across the world.
It's a major milestone for artificial-intelligence research: Go is a simple game but has been notoriously difficult for computers to master because of the sheer number of potential moves. Go players believe the game relies on intuition as a strategy.
While AI programs began being able to beat humans at chess decades ago, the best Go players in the world have always been able to outsmart Go-playing software — until now.
Go is a two-player, turn-based strategy game. Each player puts down either black or white stones in an attempt to outmaneuver and surround the other player. It's easy to pick up but takes years to master.
Demis Hassabis, the CEO and cofounder of Google DeepMind, said in a statement: " In the past ten days, we have been lucky to witness the incredible culture and excitement surrounding Go. Despite being one of the oldest games in existence, Go this week captured the public’s attention across Asia and the world.
"We thank the Korea Baduk Association for co-hosting the match, and thank all of you who watched. And of course, we want to express our enormous gratitude towards Lee Sedol, who graciously accepted the challenge and has been an incredible talent to watch in every game. Without him we would not have been able to test the limits of AlphaGo.
He continued: "We wanted to see if we could build a system that could learn to play and beat the best Go players by just providing the games of professional players. We are thrilled to have achieved this milestone, which has been a lifelong dream of mine. Our hope is that in the future we can apply these techniques to other challenges — from instant translation to smartphone assistants to advances in health care."
Lee said he was "regretful" about the result, adding that he has "more study to do."
Michael Redmond, English commentator and Go professional, said: "It was difficult to say at what point AlphaGo was ahead or behind, a close game throughout.
"AlphaGo made what looked like a mistake with move 48, similar to what happened in game four in the middle of the board. After that AlphaGo played very well in the middle of the board, and the game developed into a long, very difficult end game."
Redmond added: "AlphaGo has the potential to be a huge study tool for us professionals, when it’s available for us to play at home."
Following the victory, Hassabis wrote on Twitter that it was "one of the most incredible games ever."
#AlphaGo wins game 5! One of the most incredible games ever. To comeback from the initial big mistake against Lee Sedol was mind-blowing!!!
— Demis Hassabis (@demishassabis) March 15, 2016
After the third game, Lee apologised for not being able to satisfy people's expectations. "I kind of felt powerless," he said. "When I look back on the three matches, even if I were to go back and redo the first match, I think I would not be able to win because I misjudged AlphaGo."
The tournament has been closely watched by the most senior people at Alphabet and Google. Alphabet president Sergey Brin attended the third game, while Alphabet chairman Eric Schmidt was there for the first.