Ray Tomlinson

Network email. Messages could already be left for users of the same computer. In 1971 Tomlinson, an engineer at Bolt Beranek and Newman, adapted a file-transfer program to deliver them between machines on the ARPANET, and chose the at sign to separate the user's name from the host's. Email quickly became the network's most used application, and his addressing convention is still universal. He died in 2016.