Answer: Checkers

When it comes to classic board games like Chess, Go, Backgammon, and Checkers, there are a staggering number of potential moves in these games. On a standard competition size Go board, for example, there are potentially 10^48 moves which puts solving the game beyond the reach of our current computing capabilities.

Among such cerebral and classic games, only one has been completely solved: Checkers. In 2007, computer scientist Jonathan Schaefer completed a 19-year quest to solve all the possible moves in the game of checkers—5*10^20 potential legal positions possible. Unlike IBM’s computing system Deep Blue that uses enormous amounts of computing horsepower to analyze future moves on the fly (as completely solving the chess board is still out of reach), Schaefer’s system Chinook evolved over years of slowly crunching through the positions and potential endgames until it had learned nearly every possible move in the game.

Originally, the goal had simply been to design a computer that was very good at checkers. To that end, Chinook was doing quite well. By the 1990s, it was consistently beating top players and eventually it faced off against Marion Tinsley (not just the world champion at the time, but an absolutely legendary player who dominated the game of checkers for forty straight years). Chinook did quite well against Tinsley, but their series of six games all ended in draws. Shortly after that, Tinsley fell ill and passed away, leaving an enormous void in the world of checkers and in Schaefer’s plans to design a checkers-playing computer that could beat the world’s greatest player.

Faced with no suitable mega-champion to defeat, Schaefer did the only thing that was left to do: solve the game and effectively beat checkers itself. In 2017, he explained in an interview with The Atlantic:

From the end of the Tinsley saga in ’94–’95 until 2007, I worked obsessively on building a perfect checkers program. The reason was simple: I wanted to get rid of the ghost of Marion Tinsley. People said to me, ‘You could never have beaten Tinsley because he was perfect.’ Well, yes, we would have beaten Tinsley because he was only almost perfect. But my computer program is perfect.

Schaefer’s program is, in fact, perfect. When pitted against itself both sides play perfectly and every game ends in a draw.