The purpose of the following paper is to identify what kind of mythical creature Aeschylus’ γρυπαίετος (‘griffin–eagle’) that caused such a scandal for ‘Euripides’ in Aristophanes’ Frogs 928–930 (= Aesch. fr. inc. fab. 422 R.) was. The term has usually been interpreted in three ways: (a) as a poetic form of ‘eagle’; (b) as a poetic form of ‘griffin’; (c) as ‘eagle of the griffin species’. The testimony of Aristophanes’ Frogs and vase-painting suggests that it may have been an idiosyncratic, archaic type of griffin, called by modern specialists ‘griffin-bird’ and characterised by having two legs, not four, and the body of a bird, not a lion. This fantastic creature appeared quite frequently on Archaic black-figure vases in Athens, but had completely disappeared by the end of the 6 th century BC. As a result, its appearance would be unknown to Aristophanes’ public, making the term γρυπαίετος impossible to make out (Ra. 930). Thus, the following paper suggests that Aeschylus’ γρυπαίετος (‘griffin-eagle’) is a fabulous composite beast made up of griffin and eagle parts, as its name suggests: a griffin head (with an open hooked beak, long pointed ears, a protuberance or horn over the eyes, and a curl or plume falling down one side of the neck) crowning an eagle body (two-legged, feathered, with wings and talons).