Possible Clues:

• Greek philosopher who was a student of Socrates
• Ancient Greek philosopher and teacher of Aristotle
• Philosopher who tutored Aristotle
• Republic's author about to abandon army group
• 'Allegory of the cave' philosopher
• Greek author of the "Republic"
• Founder of the Academy
• Whom Nietzsche liked not
• Philosopher inserting line in page, odd selection for author
• Source of ancient dialogues