Final answer:
Aristotle, a student of Plato, founded the Lyceum, a school of philosophy in Athens. Cleisthenes was the Athenian leader instrumental in founding democracy in Athens.
Step-by-step explanation:
The Greek philosopher who opened a school of philosophy was Aristotle. He was a student of Plato at the Academy and later founded his own school at the Lyceum in Athens. Aristotle disagreed with Plato on the nature of forms and ideas, arguing that the material universe and the sensory experiences it provides are essential for genuine understanding.
Athenian leader Cleisthenes played an instrumental role in the founding of a democracy in Athens in the late sixth century BCE. His reforms included reorganization of the polis into demes, which weakened the power of aristocratic families and allowed a broader portion of the citizenry to participate in governance.