2007-02-23: No one person invented the Internet as we know it today. However, certain major figures contributed major breakthroughs:
Leonard Kleinrock was the first to publish a paper about the idea of packet switching, which is essential to the Internet. He did so in 1961. Packet switching is the idea that packets of data can be "routed" from one place to another based on address information carried in the data, much like the address on a letter. Packet switching replaces the older concept of "circuit switching," in which an actual electrical circuit is established all the way from the source to the destination. Circuit switching was the idea behind traditional telephone exchanges.
Why Packet Switching Matters
The big advantage of packet switching: a physical connection can carry packets for many different purposes at the same time, depending on how heavy the traffic is. This is much more efficient than tying up a physical connection for the entire duration of a phone call. And for services like the World Wide Web, where traffic comes in bursts, it's essential.
What if Google needed a separate modem and phone line to talk to every user, like an old-fashioned BBS (Bulletin Board System)? Handling millions of users would be prohibitively expensive.
With packet switching, packets destined for thousands or millions of users can share a single physical connection to the Internet.
J.C.R. Licklider was the first to describe an Internet-like worldwide network of computers, in 1962. He called it the "Galactic Network."
Larry G. Roberts created the first functioning long-distance computer networks in 1965 and designed the Advanced Research Projects Agency Network (ARPANET), the seed from which the modern Internet grew, in 1966.
Bob Kahn and Vint Cerf invented the Transmission Control Protocol (TCP) which moves data on the modern Internet, in 1972 and 1973. If any two people "invented the Internet," it was Kahn and Cerf - but they have publicly stated that "no one person or group of people" invented the Internet.
Radia Perlman invented the spanning tree algorithm in the 1980s. Her spanning tree algorithm allows efficient bridging between separate networks. Without a good bridging solution, large-scale networks like the Internet would be impractical.