Which Athenian tyrant significantly restructured Athenian tribes into units called demes?

The Athenian tyrant who significantly restructured Athenian tribes into units called demes was Cleisthenes. His reforms, known as the Cleisthenic reforms, took place in the late 6th century BCE and are often referred to as a foundational moment in the development of Athenian democracy.

By creating demes, which were local units or communities, Cleisthenes aimed to break the power of traditional tribal affiliations and foster loyalty to the city-state of Athens as a whole. This restructuring not only helped to diminish the influence of aristocratic factions but also increased the engagement of ordinary citizens in the political process. Citizens were assigned to one of the new demes, which then participated in the broader democratic institutions of Athens.

Additionally, Cleisthenes introduced other reforms that expanded the political power of the citizenry, laying the groundwork for Athenian democracy as it later flourished, particularly under leaders like Pericles. This transformation contributed to a more equitable political structure, allowing for greater participation among diverse social groups in Athens.