Cleisthenes, fl. 510 B.C., Athenian statesman. He was the head of his family, the Alcmaeonidae, after the exile of Hippias, and with Spartan help had made himself undisputed ruler of Athens by 506 B.C. He established a more democratic constitution by weakening the clan system and the local parties and by organizing the districts into political rather than social divisions. The Alcmaeonidae thus became leaders of a democratic party, a reorientation making them anti-Spartan instead of pro-Spartan as earlier. An attempt of his rival, Isagoras, to overturn the reforms of Cleisthenes after Cleisthenes had been sent into exile failed, and Cleisthenes was recalled.