A Thestral is a breed of winged horse, but its appearance is strikingly different from what one might expect. They possess a skeletal, black-hided body, making them appear gaunt and spectral. Their heads are reptilian, featuring large, leathery, bat-like wings that sprout from their withers. Perhaps their most unnerving feature is their white, pupil-less eyes, which give them a blank, ghostly stare. Due to their macabre appearance and association with death, Thestrals have an undeserved reputation in the wizarding world as omens of misfortune or evil. In reality, they are intelligent and loyal creatures.
The most defining characteristic of a Thestral is its visibility. They are visible only to individuals who have witnessed another person's death firsthand and have come to emotionally comprehend the finality of what they saw. For example, Harry Potter was unable to see them for years, even after witnessing his mother's murder as an infant, because he had no true understanding of the event. He only gained the ability to see them after witnessing the death of Cedric Diggory and spending the summer processing his grief. Others who could see them include Luna Lovegood, who saw her mother die, and Neville Longbottom, who witnessed his grandfather's death.
For centuries, Thestrals have been widely misunderstood by the wizarding community and considered bad omens. According to Rubeus Hagrid, Britain's only domesticated herd resides at Hogwarts, tamed by him for use in his Care of Magical Creatures classes and for pulling the school carriages. The primary and most consistent use of Thestrals in the series is to pull the “horseless” carriages that transport students from Hogsmeade Station to Hogwarts Castle at the beginning and end of each school year. This created a strange experience for the majority of students, who felt the carriages moving on their own, unaware of the creatures pulling them.
Thestrals first appear in Harry Potter and the Order of the Phoenix. Their reveal to Harry Potter is a significant moment, symbolizing his maturation and the inescapable trauma he carries after the events in the graveyard at Little Hangleton. They serve as a physical manifestation of the boundary between innocence and the experience of loss. In that same book, six Thestrals provide the crucial transport for Harry, Ron Weasley, Hermione Granger, Ginny Weasley, Neville Longbottom, and Luna Lovegood to fly to the Department of Mysteries to rescue Sirius Black. During the Second Wizarding War, Thestrals were used by the Order of the Phoenix as mounts during the Battle of the Seven Potters. Later, they fought in the Battle of Hogwarts, attacking Voldemort's Giants alongside the Hippogriff Buckbeak. The revelation in Harry Potter and the Deathly Hallows that the Elder Wand contains a Thestral hair core elevates the creature's status from a misunderstood beast to a source of immense magical power.