Contemporary accounts played the story as a Man vs. Machine battle, the quick wits of a human versus the brute computing power of a supercomputer. But Tinsley and Schaeffer both agreed: This was a battle between two men, each having prepared and tuned a unique instrument to defeat the other. Having been so dominant against humans for so long, Tinsley seemed to thrill at finally having some entity that could give him a real game. He had volunteered to play friendly matches against the computer in the run-up to their two world championship matches. And Schaeffer, though he was a bull-headed young man, had become the most effective promoter of Tinsley’s prowess and legacy.

But there, in that hall, a quirk of human development was troubling Tinsley. His stomach hurt. The pain was keeping him up all night. After six games—all draws—he needed to see a doctor. Schaeffer took him to the hospital. He left with Maalox. But the next day, an X-ray revealed there was a lump on his pancreas. Tinsley understood his fate.

He withdrew. Chinook became the first computer program in history to win a human world championship. But Schaeffer was crushed. He’d devoted years of his life to creating a program that could beat the best checkers player ever, and just as he was about to realize this dream, Tinsley quit. Seven months later, Tinsley died, never having truly lost a match to Chinook.

And that would lead Schaeffer to undertake a 13-year computational odyssey to exorcise the man’s ghost. With Tinsley gone, the only way to prove that Chinook could have beaten the man was to beat the game itself. The results would be published July 19, 2007, in Science with the headline: Checkers Is Solved.

“From the end of the Tinsley saga in ’94–’95 until 2007, I worked obsessively on building a perfect checkers program,” Schaeffer told me. “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.”

* * *

Jonathan Schaeffer did not begin his career intending to solve checkers. He was a chess player, first. Good, not great. But he also loved computers—and had done a Ph.D. in computer science, so he decided to build a chess-playing program. He called it Phoenix and it was one of the better chess programs of many that were created in the 1980s. In 1989, he “crashed and burned” at the World Computer Chess Championships, however. At the same time, the team that would form DeepBlue, the chess software that would eventually defeat Kasparov, was coming together. Schaefer realized he would never build the world computer champion.

A colleague suggested that perhaps he should try checkers, and thrillingly, with just a few months of work, his software was good enough to bring to the Computer Olympiad in London to compete against other checkers-playing bots. And it was there that he began to hear about Marion Tinsley, the great.