On May 11, 1997, chess grandmaster Garry Kasparov resigns after 19 moves in a game against Deep Blue, a chess-playing computer developed by scientists at IBM. This was the sixth and final game of their match, which Kasparov lost two games to one, with three draws.

Kasparov, a chess prodigy from Azerbaijan, was a skillful chess player from childhood. At 21, Kasparov played Anatoly Karpov for the world title, but the 49-game match ended indecisively. The next year, Kasparov beat Karpov to become the youngest world champion in history. With a FIDE (Federation International des Echecs) score of 2800, and a streak of 12 world chess titles in a row, Kasparov was considered the greatest chess player in history going into his match with Deep Blue.

Chess-playing computers had existed since the 1950s, but they initially saw little success against accomplished human players. That changed in 1985, when Carnegie Mellon doctoral student Feng-hsing Hsu developed a chess-playing computer named “Chiptest” that was designed to play chess at a higher level than its predecessors. Hsu and a classmate went to work for IBM, and in 1989 they were part of a team led by developer C.J. Tan that was charged with creating a computer capable of competing against the best chess players in the world. The resulting supercomputer, dubbed Deep Blue, could calculate many as 100 billion to 200 billion positions in the three minutes traditionally allotted to a player per move in standard chess.

Kasparov first played Deep Blue in 1996. The grandmaster was known for his unpredictable play, and he was able to defeat the computer by switching strategies mid-game. In 1997, Kasparov abandoned his swashbuckling style, taking more of a wait-and-see approach; this played in the computer’s favor and is commonly pointed to as the reason for his defeat.

The last game of the 1997 Kasparov v. Deep Blue match lasted only an hour. Deep Blue traded its bishop and rook for Kasparov’s queen, after sacrificing a knight to gain position on the board. The position left Kasparov defensive, but not helpless, and though he still had a playable position, Kasparov resigned—the first time in his career that he had conceded defeat. Grandmaster John Fedorowicz later gave voice to the chess community’s shock at Kasparov’s loss: “Everybody was surprised that he resigned because it didn’t seem lost. We’ve all played this position before. It’s a known position.” Kasparov said of his decision, “I lost my fighting spirit.”