Donald Watts Davies was a Welsh computer scientist who co-invented the packet-switching technology. Born in the Rhondda Valley, he later studied at Imperial College London, and spent most of his career conducting research at the UK's National Physical Laboratory. When Davies first began working at National Physical Laboratory, he worked alongside the pioneer of computer science, Alan Turing. It's reputed that Davies highlighted some errors within Turing's theoretical programming, much to the chagrin of the aforementioned computer scientist.
Turing, at that time, was working on a project to develop a automatic computing engine. Ambitious in the scope, it failed to meet expectation, which led to Turing's exit. Davies took over the project, limited it's ambitions and delivered a working ACE computer by the early 1950's. Davies became interested in researching communication between computers in the 1960's. While visiting MIT in the US, he noticed some problems in their research, and came back to the UK to develop packet-switching. By the end of the 1960's, Davies had built a packet-switching network for the National Physical Laboratory, named Mark I.
While Davies was developing the Mark I network, his work had inspired the Advanced Research Project Agency of America to develop their own packet-switching network. Named ARPANET, it evolved to become the Internet. Packet-switching is still a part and parcel of how the Internet functions. Davies spent most of his career working for the National Physical Laboratory. However, he did spend time in the private sector, working as an advisor for computer security.