Which king of Persia attempted to invade Greece but was defeated at the Battle of Marathon?

The king of Persia who attempted to invade Greece and was defeated at the Battle of Marathon is indeed Darius the Great. His invasion in 490 BCE was part of the larger conflict between the Persian Empire and the Greek city-states. The Battle of Marathon was significant not only for its outcome but also because it marked the first major Greek victory in the Persian Wars. Darius aimed to expand his empire and punish Athens for its support of the Ionian revolt against Persian rule. The overwhelming victory of the Athenian forces at Marathon inspired confidence in the Greek city-states and showcased the effectiveness of their hoplite soldiers. This battle laid the groundwork for future confrontations, such as those at Thermopylae and Salamis, during the ongoing struggle against Persia.