Brute force
Deep Blue did not think like a human. It had special chess chips and searched a huge number of moves ahead, using rules from grandmasters. After the match Kasparov suspected IBM of human help and demanded a rematch. IBM dismantled the machine.
From Kempelen to AlphaZero
Chess-playing machines have fascinated people since 1770, when Wolfgang Kempelen from Bratislava presented his “Turk”. In 2017 DeepMind's AlphaZero taught itself chess in a few hours just by playing against itself, and beat the best classical programs. See Deep learning and neural networks.
Today
A chess app on a phone now plays better than any human. Chess players use it for training and for analysing games.