Random-play Monte-Carlo was the first algorithm that lead to good computer Go software, before neural network. It was around 2008 I think. Before that, pattern-base algos were really, really bad (like, barely above human beginner level).

I'm not a mathematician, but the paper itself was a real beauty. I remember vividly the parameter that balanced "exploitation" of apparently-good paths, and "exploration" of unknown/apparently-bad path. I used it in many analogies discussing innovation programs within large companies.