The Turing Machine
It baffles me that any computable problem can be solved with such a simple foundation. It's crazy to think that something so basic could be the foundation for all the fancy computers we have now. But I guess that's how technology works, right? You start with something simple and build on it until you get something super advanced.
As the professor stated in class: combine information theory with Turing's 'universal computer' and you have a way for a machine computer to simulate any of the work a human computer could do.
Fascinating...