The hippogryph, living far beyond the seas in the Rhiphaean Mountains, is the result of the rare breeding of a male gryphon and a filly. It has the head, wings and front legs of a gryphon, and the back and hind legs of a horse. It is a large powerful creature that can move through the air more swiftly than ligthning.
Griffins are traditionally regarded as having an antipathy for horses. Therefore the hippogriff, being the offspring of a horse and a griffin, is a doubly impossible being.
The Hippogriff figured in several of the legends of Charlemagne as a mount for some of the knights.