Ray Tomlinson chose the @ symbol to separate a user from a host in email addresses.
In 1971, Tomlinson was working on ARPANET email systems at Bolt, Beranek and Newman. He modified an existing program so that messages could be sent between different networked computers, rather than only between users of the same machine. He needed a character that was unlikely to appear in a person’s name.
Tomlinson selected @ because it already meant “at” in commercial and accounting contexts. An address such as [email protected] could therefore be read as a user “at” a particular host or domain. The symbol was available on the keyboard and had a useful meaning without being common in names.
The @ sign was not invented for email; it has much older commercial and linguistic uses. Tomlinson’s key contribution was making it part of the standard Internet email-address format.