Ephialtes is an ancient Athenian politician and an early leader of the democratic movement there.

In the late 460s BCE, he oversees reforms that diminished the power of the Areopagus, a traditional bastion of conservatism, and which are considered by many modern historians to mark the beginning of the "radical democracy" for which Athens would become famous.

These powers included the scrutiny and control of office holders, and the judicial functions in state trials.

He introduced pay for public officeholders, reduced the property qualifications for holding a public office, and created a new definition of citizenship.

Ephialtes, however, would not live to participate in this new form of government for long.

In 461 BCE, he was assassinated at the instigation of resentful oligarchs, and the political leadership of Athens passed to his deputy, Pericles.