Centaur

Centaurs were creatures that were part-human and part-horse. They had a place in Earth's mythology, although many accounts depicted them as really existing, either on Earth or on other planets.

History
On Caligaris Epsilon Six, the Eleventh Doctor and Amy found a centaur. The Doctor also remarked they were hunted by humans, which led to their extinction. (COMIC: A Fairytale Life)

A centaur was present at the First Auction in Heaven and bid the Moon of Troth on the the Frozen Battle of Cratosi Fields, one of the pricier items on sale. (PROSE: Going Once, Going Twice)

Dagmar Ruskovitch was able to transform from a human form to that of a centaur. (COMIC: Herald of Madness)

In popular culture
The Fifth Doctor knew a version of the story of Noah's Ark in which Noah had to leave behind unicorns, centaurs, basilisks and many other such animals. (PROSE: Perfect Day)

Centaur-like species
The Doctor met several alien species which resembled centaurs. These included the Klim, (COMIC: The Dalek Revenge) Firbolg, (PROSE: Cat's Cradle: Witch Mark) Unon, (COMIC: Weapons of Past Destruction) and Aquabi. (AUDIO: Pest Control)

Cheiron, one of the centaurs escaping from Tír na n-Óg, was burnt to death. Witnesses were told it was an escaped lab experiment. (PROSE: Cat's Cradle: Witch Mark)