Cleisthenes
Cleisthenes, or Clisthenes (latter part of the sixth century B.C.), an Athenian statesman and reformer credited with establishing democratic government in the Athenian city-state. Cleisthenes was one of the aristocrats exiled from Athens while Pisistratus and his sons ruled as tyrants, 560–510 B.C. When the tyranny was overthrown, Cleisthenes opposed the restoration of aristocratic rule. About 506 B.C. he revised the Athenian constitution and reorganized the government.
Citizen registration rolls were made out in each deme(an administrative district that was usually a village or part of a city). A number of demes from different areas were combined into a larger grouping called a phyle(tribe). By thus mingling the various social classes and geographical groups, Cleisthenes made it difficult for special-interest parties to be formed. There were 10 phylai(tribes), each of which sent 50 representatives, chosen annually by lot, to form the boule(council), an important new unit of government. With some refinements added later, this governmental structure gave Athens a democracy such as the world had never known.
According to tradition, Cleisthenes also originated the system of ostracism. However, nothing definite is known of him and his work beyond the constitutional reform.