Achilles Tatius was a Greek author from Alexandria, Egypt, who lived during the 2nd century CE, a period of the Roman Empire. He is traditionally identified as a sophist, meaning he was trained in the rhetoric and literary culture that flourished in the Greek-speaking world at that time. Beyond this, almost no secure facts about his life are known. A later Byzantine source claims he converted to Christianity and became a bishop, but modern scholars generally consider this an unreliable tradition.

He is famous as the author of the ancient Greek novel Leucippe and Clitophon, which is his only surviving work. This novel follows the romantic adventures and numerous misfortunes of its central couple, featuring pirates, shipwrecks, and dramatic separations. The story is known for its elaborate, descriptive style and its use of first-person narration.

Achilles Tatius is historically important as one of the principal authors of the ancient Greek novel. Leucippe and Clitophon is a key example of this popular genre, which combined exciting plots with themes of love, chastity, and fortune. The work was preserved through the Byzantine period and later influenced the development of European prose fiction.