Leonard Kleinrock is a computer scientist whose theoretical work on data networks and whose UCLA laboratory place him at the origin of the Internet. According to his Internet Hall of Fame profile, he “pioneered the mathematical theory of packet networks, the technology underpinning the Internet,” developing this work as a graduate student at MIT in the early 1960s and earning his Ph.D. there in 1963. His use of queueing theory to analyze how messages flow and wait in a shared communication network provided some of the earliest formal tools for understanding network performance.
In 1969, Kleinrock’s laboratory at UCLA was selected as the site of the first node of the ARPANET. When his host computer was connected to its Interface Message Processor (IMP), UCLA became node one of the network that would grow into the Internet.
The network’s first host-to-host message was sent from that lab on October 29, 1969. As Kleinrock recounts in his firsthand account of the event, he and his student programmer Charley Kline attempted to log in to the Stanford Research Institute machine over the new link. They “succeeded in transmitting the ‘l’ and the ‘o’ and then the system crashed,” so the inaugural transmission across the network was the two letters “lo,” as in “lo and behold.” A full login succeeded about an hour later. The moment is documented in the scanned UCLA IMP log for that date.
Kleinrock has remained a Distinguished Professor of Computer Science at UCLA and is widely honored as one of the fathers of the Internet, sharing recognitions such as the Charles Stark Draper Prize with Vinton Cerf, Robert Kahn, and Lawrence Roberts, and receiving the National Medal of Science. His combination of foundational theory and the hands-on birth of the ARPANET in his own laboratory makes him a singular figure in networking history.