Centaur

A Centaur (Κένταυρος in Ancient Greek) is a half horse, half human.

History
The Centaurs are best known for their fight with the lapithae, caused by their attempt to carry off Hippodamia and the rest of the Lapith women, on the day of her marriage to Pirithous, king of the Lapithae, himself the son of Ixion.

Centaurs were notorious for being overly indulgent drinkers and carousers, given to violence when intoxicated, and generally uncultured delinquents. Each Centaur was also wild and lusty, except for the most well-known centaur, Chiron. True centaurs were born of sun and raincloud, until the female centaurs (called Centauresses) came from some normal horses, and centaurs started out like normal creatures, from conceived from baby to adult. Chiron was another exception. He was born from Kronos and the nymph Philyra. He was half-horse because Kronos was half-horse when he was with Philyra.

The Lightning Thief
One known serious centaur is Chiron, the activities director at Camp Half-Blood and appears throughout the rest of the series. In the train to Denver, Percy sees a family of centaurs hunting next to the train. A little boy centaur smiles and waves at him.

The Sea of Monsters
When Percy was fighting with Luke, The centaur organization, the Party Ponies (Florida Chapter) made an appearance.

The Battle of the Labyrinth
At least one centaur is known to have been defeated by a Giant under orders from Antaeus in The Battle of the Labyrinth.

The Last Olympian
The Party Ponies, commanded by Chiron, assist the demigods in The Battle of Manhattan, though Percy sees none other than Chiron at the end of the battle. He deduces that they were either killed or ran away.

The Son of Neptune
The army of monsters that attacks Camp Jupiter has another breed of centaurs who seem to enjoy killing demigods. These centaurs appear to be a different breed from the Party Ponies, their horse halves being palamino and horns sticking out of their heads. They were all either killed or fled from the battle.