If it weren't for Alan Turing, the modern computer would not exist. He invented a code breaking machine during WWII known as the Bombe, which is considered by most to be the first general purpose computer. His paper titled "On Computable Numbers, with an application to the Entscheidungs problem" serves as the foundation for modern computing sciences. While he didn't invent the computer you're reading this list on, without him we wouldn't have modern computers.