A centaur was mythological creature that was part-human and part-horse.
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)
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)
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)