Forty years ago, Vint Cerf and Bob Kahn got together in the summer of 1973 and created the first specification for ARPA's inter-networking protocol laying the foundation for connecting networks implemented using different protocols together. Thus was born the Transmission Control Protocol, TCP.
TCP was not the first or only protocol implemented. But over the next two decades it emerged as the undisputed standard for inter-net-working, or connecting computer networks to each other: the one we call the Internet.