Thestrals are fictional large winged horses introduced in the novel Harry Potter and the Order of the Phoenix.

Thestrals are the most elusive (and least horse-like) breed of magical horse. They are invisible to all who haven't 'seen death', which requires not only witnessing a death, but having the event sink in. For those who have, their skeletal appearance is no less morbid. They have an understandable but undeserved reputation as evil omens.

Despite their looks, thestrals are living creatures. They are either carni- or omnivores, and predators; they have fangs, are attracted by the smell of blood and will occasionally go after birds. According to Hagrid, they will not attack a human-sized target without provocation. Their wings are capable of very fast flight for at least several hours at a time, though they usually spend their time on the ground, and they have an excellent sense of direction.

The horses are at least semi-domesticable, provided that a willing trainer can be found. Thestrals can be used to pull loads, and are a serviceable if very uncomfortable mode of transportation for someone with enough nerve.

Hogwarts has a herd of the animals that dwells in the nearby forest . Thestrals pull the carriages that transport students from from the railway station at Hogsmeade to the school at the beginning of each term, and back again at the end of the year. Prior to Harry Potter and the Order of the Phoenix, Harry and his friends (as well as the readers) believed that the carriages were bewitched to move on their own. However, at the end of Harry Potter and the Goblet of Fire, Harry witnesses Cedric Diggory's death, and gains the ability to see the thestrals. Since he does not fully accept Cedric's death until the beginning of the following year, he cannot see them on his journey to the railway station at the end of his fourth year.

Luna Lovegood saw her mother die when she was nine, and has therefore been able to see the thestrals since she arrived at Hogwarts; she assumed that everybody else could as well.

Care of Magical Creatures students learn about thestrals in their seventh year - or fifth, if their teacher is Hagrid. Thestrals are listed under in the Winged Horses section in Fantastic Beasts and Where to Find Them.