Ray Tomlinson created networked email, gave the @ symbol its modern meaning, and then declined to own a cell phone. Born on April 23, 1941, in Amsterdam, New York, and raised in the village of Vail Mills, he was the son of a carpet mill worker and a dry cleaner’s employee. He studied electrical engineering at Rensselaer Polytechnic Institute, did a co-op with IBM, and went on to MIT, where the early video game Spacewar showed him that computers could respond to people in real time.

This episode follows him to Bolt, Beranek and Newman in 1967, the firm building the ARPANET. In 1971 he was asked to make a routine update to SNDMSG, a program that could only leave messages for users on the same machine. Instead he grafted it onto his CPYNET file transfer code so a message could cross the network. Nobody had asked for it, and he told a colleague not to tell anyone. The episode also covers his work on the TCP three-way handshake and his dry, unhurried view of the world he helped wire.

• Tomlinson picked the @ sign from his Model 33 Teletype keyboard because it was an obscure bookkeeping symbol unlikely to appear in a username or system command.
• The first networked email traveled between two machines sitting side by side in the same room at BBN, and he never saved the forgettable test text.
• In 2010 the Museum of Modern Art acquired the @ sign for its architecture and design collection and credited Tomlinson for its modern use.
• He insisted on spelling email without a hyphen, joking that he wanted to conserve the world’s supply of hyphens.
• He died of a heart attack on March 5, 2016, at age 74 in Lincoln, Massachusetts, and an asteroid, 10108 Tomlinson, carries his name.