March 2016: AlphaGo Defeats Lee Sedol

One of the most celebrated AI achievements occurred when Google DeepMind’s AlphaGo defeated Lee Sedol, a world champion in the ancient board game Go, in a five-game match held from March 9–15, 2016. AlphaGo won 4–1, showcasing the power of deep reinforcement learning and convolutional neural networks. Go’s complexity—featuring more possible moves than atoms in the observable universe—had long been a benchmark for AI, and this victory marked a leap forward in strategic reasoning capabilities. Most observers had predicted such proficiency was still a decade away, making this a landmark moment.