By November 1973, Metcalfe and his colleagues had their first network up and running. He continued to develop the design further, hoping to expand it beyond Xerox, but executives were slow to commercialize the new technology. By 1979, Metcalfe had had enough. He left PARC and founded his own company, 3Com, to do what Xerox wouldn’t. “Humble was not a word that you associated with Bob,” said Vint Cerf, an internet pioneer now at Google. “He took this idea and ran with it.”

Not long after striking out on his own, Metcalfe convinced representatives from Xerox, Intel and the now-defunct Digital Equipment Corporation to adopt Ethernet as an open industry standard for local networking. Other companies promoted their own technologies, but Ethernet eventually won out, due in large part to its simplicity and Metcalfe’s early push for standardization.

In 1990, Metcalfe left 3Com and became a pundit and tech columnist. It was the second time he had grown restless after about a decade in one career, and it wouldn’t be the last — he went on to work as a venture capitalist and later as a professor at the University of Texas, Austin. Metcalfe has a theory for what drives him to make such dramatic changes. “You start out not knowing anything, and then you go up the learning curve, and then you know everything,” he said, tracing out a curve with his finger. He pointed at the middle of the curve and added, “I have discovered through experience that the fun part to be on is right here.”

Ethernet has also adapted over the years, and few of the original technical details remain. But it has continued to play an indispensable role as the domestic plumbing for the networks of personal computers we now take for granted. “It was Ethernet that made that possible,” Cerf said. “It really was a hugely enabling technology.”

Less than a year ago, Metcalfe made yet another career change at the age of 76. He’s now a research affiliate at MIT, studying the application of supercomputers to complex problems in energy and other fields. “I’m still at the early part of the learning curve,” he said. “I don’t know much, but I’m working to fix that.”