Centaur

Centaurs are six-limbed creatures, having the body of a horse with the upper body of a human in place of the horse's head. In the one known example, the ears are also equine, and the face is noticeably elongated.

From the Word of God page:

"You don't want to try to ride a centaur unless you know them well or you were specifically asked to hop on. It's rude otherwise (just as it would be rude to jump on someone's back if you didn't know who the hell they were)."

Examples: Zech Smith