Thestrals are large winged horses in the Harry Potter series of novels by J. K. Rowling. They are introduced in Order of the Phoenix.
Thestrals are the most elusive and least horse-like breed of magical horse. They have earned an undeserved reputation as omens of evil. They are visible only to those who have witnessed and accepted a death, and their appearance is skeletal, fleshless. They are described in Harry Potter and the Order of the Phoenix as having "blank, white, shining eyes," a "dragonish face", "long, black manes", "great leathery wings", and the "skeletal body of a great, black, winged horse".