[ahartmetz]

Also Konrad Zuse, frequently ignored in the anglosphere. He is one of ~two people with a credible claim to building the first freely programmable (Turing-complete) computer. His first few computers were mechanical, later models electrical.

[Oarch]

Going back even further, I'd argue Gottfried Leibnitz was one of the first to grasp the fundamental problems of building a computer.