Cleisthenes (Greek: Κλεισθένης, also Clisthenes or Kleisthenes) was a noble Athenian of the Alcmaeonid family. He is credited with reforming the constitution of ancient Athens and setting it on a democratic footing in 508/7 BC. For these accomplishments, historians refer to him as "the father of Athenian democracy." Also, he was credited for increasing power of assembly and he also broke up power of nobility for Athens. Cleisthenes called these reforms isonomia ("equality vis à vis law", iso=equality; nomos=law), instead of demokratia. In order to forestall strife between the traditional clans, which had led to the tyranny in the first place, he changed the political organization from the four traditional tribes, which were based on family relations, into ten tribes according to their area of residence (their deme). Most modern historians suppose there were 139 demes (this is still a matter of debate), organized into thirty groups called trittyes ("thirds"), with ten demes divided among three regions in each trittyes (a city region, asty; a coastal region, paralia; and an inland region, mesogeia). Cleisthenes also abolished patronymics in favour of demonymics (a name given according to the deme to which one belongs), thus increasing Athenians' sense of belonging to a deme. He also established legislative bodies run by individuals chosen by lottery, a true test of real democracy, rather than kinship or heredity. He reorganized the Boule, created with 400 members under Solon, so that it had 500 members, 50 from each tribe. He also introduced the bouletic oath, "To advise according to the laws what was best for the people". The court system (Dikasteria — law courts) was reorganized and had from 201–5001 jurors selected each day, up to 500 from each tribe. It was the role of the Boule to propose laws to the assembly of voters, who convened in Athens around forty times a year for this purpose. The bills proposed could be rejected, passed or returned for amendments by the assembly.
Cleisthenes was the uncle of Pericles' mother Agariste and of Alcibiades' maternal grandfather Megacles.