A network of networks
In the early 1970s several networks existed: ARPANET, as well as radio and satellite networks. Each spoke a different language. Kahn and Cerf designed a common set of rules, by which data is split into packets carrying an address and reassembled at the destination, whatever network they travel through.
The internet's D-Day
ARPANET switched over to TCP/IP on 1 January 1983. This day is often called the internet's birthday. The protocol was open and free, and that's why the whole world adopted it.
What they do today
Bob Kahn founded the research organisation CNRI. Vint Cerf has worked at Google since 2005 as its "Chief Internet Evangelist" and also works on an interplanetary internet for space probes.