The world is experiencing a boom in artificial intelligence (AI). It's everywhere. In just a few years, computers have learned to paint a picture, write a novel, translate languages and consume the entire internet.

But how we got here goes back decades to two men who couldn't agree on the best way to teach a thinking machine.

The AI world was divided. Then a new kind of machine beat a human at Go, a game it was never supposed to be able to win.