Conway's Game of Life
John Horton Conway made the Game of Life because he wanted to know if he could make an imaginary robot out of cells that would be able to get bigger.  He combined lots of ideas in math to make the rules for the game.  It is one of the first ever 'simulation games' that represent things that happen in real life.  It is important because when used in complicated math, it can look at many things like physics, biology, economics, and philosophy.