"Never try an' get a straight answer out of a centaur. Ruddy stargazers. Not interested in anythin' closer'n the moon."
-- Hagrid (PS15)
Centaurs are intelligent creatures with the head and torso of a human joined to the body of a horse. They have a rich history and are known for being skilled in healing, divination and astronomy.
Centaurs are proud and territorial creatures and are equally mistrustful of Muggles and wizards alike (FB). They live in herds, typically in forests that have been appropriated by the Ministry of Magic for their use. A number of centaurs live in the Forbidden Forest, including Ronan (PS15), Bane (PS15), Magorian (OP30) and up until Harry's fifth year, Firenze (PS15, OP27). They prefer simply to observe events they have predicted instead of taking part in them (PS15). The centaurs were invited to be classified as Beings and play a role in wizarding governance, but have chosen instead to be classified as Beasts by the Ministry (FB) and do not take part in governing at all.
The word centaur comes from the Greek kentauros, the Greek name for a Thessalonian tribe of expert horsemen that at one time invaded Greece.
Centaurs figure prominently in Greek mythology. In many cases, Centaurs represent animalistic behaviour – carrying off human women, for example – but they also appear as wise teachers. The Centaurs in the Harry Potter books demonstrate both traits. Bane carries off Umbridge when she insults and attacks the herd. Firenze, on the other hand, becomes a teacher at Hogwarts, even though he is banished from the herd because of associating with wizards (The Lexicon page 55).
This creature was not invented by J.K. Rowling.