Cleisthenes ( KLYS-thin-eez; Ancient Greek: Κλεισθένης), or Clisthenes (c. 570 – c. 508 BC), was an ancient Athenian lawgiver credited with reforming the constitution of ancient Athens and setting it on a democratic footing in 508 BC. For these accomplishments, historians refer to him as "the father of Athenian democracy". He was a member of the aristocratic Alcmaeonid clan. He was the younger son of Megacles and Agariste making him the maternal grandson of the tyrant Cleisthenes of Sicyon. He was also credited with increasing the power of the Athenian citizens' assembly and for reducing the power of the nobility over Athenian politics.

In 510 BC, Spartan troops helped the Athenians overthrow the tyrant Hippias, son of Peisistratus. Cleomenes I, king of Sparta, put in place a pro-Spartan oligarchy headed by Isagoras. However, Cleisthenes, with the support of the middle class and aided by democrats, took over. Cleomenes intervened in 508 and 506 BC, but could not stop Cleisthenes and his Athenian supporters. Through Cleisthenes' reforms, the people of Athens endowed their city with isonomic institutions—equal rights for all citizens (though only free men and women were citizens)—and established ostracism as a punishment.

...