Herodotus claimed that the institution was created by Lycurgus, while Plutarch considers it a later institution. It may have arisen from the need for governors while the kings were leading armies in battle. The ephors were elected by the popular assembly, and all citizens were eligible for election. They were forbidden to be reelected. They provided a balance for the two kings, who rarely cooperated with each other. Plato called them tyrants who ran Sparta as despots, while the kings were little more than generals.
The ephors presided over meetings of the Gerousia, the oligarchic council of elders. They were in charge of civil trials, taxation, the calendar, foreign policy, and military training for young men. The year was named after one of them, like the eponymous archon of Athens. Two ephors accompanied the army in battle, and they could arrest and imprison the kings for misconduct during war. The ephors were also considered to be personally at war with the helots, so that they could imprison or execute any of them for any reason at any time without having to bring them to trial or violate religious rituals. The Ephors did not have to kneel down before the Kings of Sparta and were highly considered by the citizens, because of the importance of their powers, because of the holy role they earned throughout their functions. Since decisions were made by majority vote, this could mean that Sparta's policy could change fast, when one vote of an ephor switched. E.g. in 403 BC when Pausanias convinced three of the ephors to send an army to Attica. This was a complete turnaround to the politics of Lysander.
Cleomenes III abolished the ephors in 227 BC, but they were restored by the Macedonian king Antigonus III Doson after the Battle of Sellasia. The position existed into the 2nd century AD when it was probably abolished by the Roman emperor Hadrian.
Ephor is also the term used for a prefect at The Edinburgh Academy.
In the 1962 film The 300 Spartans, the Spartan council is shown to be composed of five members who rule Sparta along with the Spartans co-kings Leonidas and Leotychidas. Though not explicitly named as such, the members of the council appear to be the Ephors, being five in number and being able to veto decisions by the Spartan kings.
In Frank Miller's graphic novel 300 and its film adaptation, the Ephors are depicted as an apparently unelected priestly group of corrupt, diseased (leprous), inbred men who secretly betray Sparta to the Persian king Xerxes by counseling Leonidas against going to war, masking their betrayal as showing honor for the Carneian festival. Curiously, they are depicted as being keepers of an oracle that appears to at least have been inspired by the Delphic Oracle - the oracle is a young and beautiful Spartan girl who is frequently molested by her lecherous custodians.