Theognis was an archaic Greek poet from Megara, traditionally dated to the mid-6th century BCE. Ancient sources, including Plato, confirm his historical existence, though his precise origin—whether from the mainland Megara or the Sicilian colony of the same name—remains uncertain. His poetry presents him as an aristocrat who suffered exile and loss of status during political upheaval in his city. Much of his didactic verse is addressed to a youth named Cyrnus.

His surviving work is known as the Theognidea, a composite anthology of nearly 1,400 lines of elegiac poetry. A core section addressed to Cyrnus is considered the most authentic material from Theognis himself. The larger collection, however, incorporates verses by other archaic poets such as Tyrtaeus and Solon, forming a broad compilation of gnomic elegy assembled over several centuries.

The corpus is a vital source for understanding archaic Greek aristocratic values, politics, and ethics. It reflects deep anxieties about social mobility and political strife. Used as an educational text in antiquity and quoted by authors like Plato and Aristotle, the Theognidea remains central to the study of archaic elegy and early Greek social history.