Centaur

A centaur was a half-human half-horse creature.

My Little Pony
The only known centaur was Tirek, the demoniac being and dark planeswalker. Tirek hailed from an unknown region of Ponyland and founded the Midnight Castle, a kingdom under his complete control, where he used the power of the Rainbow of Darkness to convert the inhabitants into his minions.

Friendship is Magic
Centaurs hailed from the Infernal Land, a small kingdom ruled by King Vorak and Queen Haydon, a centaur and gargoyle respectively. Centaurs spoke the Common language, but with their own naming convention that often involved names ending with a "k" (Tirek, Vorak, Sendak) and seemed to be a largely peaceful, if rough, civilization that was eventually destroyed. Tirek, an immortal, became the last known centaur in the modern ages.

The centaurs had contact with Equestria and knew of and Princess Celestia, but their relations were otherwise unclear.

Abilities
Tirek and Sendak and presumably other centaurs had the ability to drain magic from their victims, becoming stronger as a result.

Equestria Girls
Centaurs are figures in the video game series, Tirek.

Known centaurs

 * . Also spelled as Tirac and Tyrek.
 * Vorak
 * Sendak
 * Elder centaur
 * Gram Gram