Buckbeak is a Hippogriff. Hippogriff are creatures that can fly; they have the front legs, wings and head of a giant eagle with the body, tail and hind legs of a horse.
They are also known to make noble companions when shown respect and Buckbeak becomes a fond pet of Hagrid's. When Buckbeak injures Draco Malfoy during Hagrid's Care of Magical Creatures class, he is sentenced to death.
Luckily Harry and Hermione are there and use the Time-Turner to save Buckbeak's life.
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