Ever since the 1500s, and for hundreds of years after, the only people who used @ were bookkeepers, who used it as a shorthand to show how much they were selling or buying goods for: for example, “3 bottles of wine @ $10 each.”
Since these bookkeepers used @ to deal with money, a certain degree of whimsical fondness for the character developed over time. In Danish, the symbol is known as an “elephant’s trunk a”; the French call it an escargot. It’s a streudel in German, a monkey’s tail in Dutch, and a rose in Istanbul. In Italian, it’s named after a huge amphora of wine, a liquid some Italian bookkeepers have been known to show a fondness for.
Even with such cute names to recommend it, though, @ languished in obscurity for three and a half centuries, only ending up on a new invention called the typewriter when salesmen realized that accountants and bookkeepers were buying them in droves.
In 1971, however, a keyboard with a vestigial @ symbol inherited from its typewriter ancestors found itself hooked up to an ARPANET terminal manned by Ray Tomlinson, who was working on a little program he’d come up with in his goofing-off time to send messages from computer to computer. Tomlinson ended up using the @ symbol as the fulcrum of the lever that ultimately ended up lifting the world into the digital age: email.