A charioteer is the person who drives a chariot — the one who holds the reins, stands in the cart, and tries not to be thrown out at the turn. In the ancient races this was a real job, and a famous charioteer could become rich and loved, rather like a sports star. In war, the charioteer often drove while a fighter beside him threw spears. The word is almost only for that old world; you would not call a taxi driver a charioteer except as a joke. Though actually, books also use it as a verb, to charioteer, meaning to drive a chariot, but you will rarely need that. The ending -eer is a “person who…” ending, but here it is firmly tied to chariot.