Aristagoras, d. 497/496 BC, was the leader of the Ionian city of Miletus in the late 6th century BC and early 5th century BC and a key player during the early years of the Ionian Revolt against the Persian Achaemenid Empire. He was the son-in-law of Histiaeus, and inherited the tyranny of Miletus from him.

Miletus was an ancient Greek city on the western coast of Anatolia, near the mouth of the Maeander River in ancient Ionia. Its ruins are located near the modern village of Balat in Aydın Province, Turkey. Before the Persian rule that started in the 6th century BC, Miletus was considered among the greatest and wealthiest of Greek cities.