The name says exactly what the cipher does. Take the Hebrew letters Aleph, Taw, Bet, Shin — the first, last, second and second-to-last letters of the Hebrew alphabet — and you get אתבש: Atbash. The name is the key legend of the cipher itself, read off its own mapping.
The oldest known uses hide inside the Hebrew Bible. The Book of Jeremiah — written around the fall of Jerusalem in 586 BC — calls Babylon Sheshach and the Chaldeans Lev-kamai; medieval commentators recognised that both are ordinary Hebrew words run through Atbash (בבל bbl → ששך ššk, כשדים kśdym → לבקמי lbqmy). Commentators such as Rashi (1040–1105) and Radak discussed these passages, which makes Atbash the oldest attested substitution cipher by a wide margin.
Scholars still argue about intent: a disguise for sensitive names, a literary game, or a scribal puzzle — the Bible's scribes left no memo. What is clear is that the alphabet-mirror was part of Hebrew scribal culture centuries before European cryptography existed, and it lived on in Jewish mysticism alongside Gematria, where letters are numbers to be rearranged.
Once generalised, Atbash is simply "reverse the collating order" — it works on Latin, Greek, Cyrillic, any ordered alphabet. Modern cryptography meets it mostly as a teaching example and a puzzle-book staple, and mathematically as the boundary case of the affine family. A cipher from the prophets, still doing service as lesson one.