The famous philosopher and author of "The Republic," advocating for a just society, was Plato. Living in ancient Greece, Plato's works explored various themes such as justice, government, and the nature of reality. In "The Republic," he outlines his vision of an ideal society governed by philosopher-kings, where citizens are assigned roles based on their abilities and education. Plato's ideas laid the groundwork for Western political theory and influenced many subsequent philosophers. His dialogues with Socrates demonstrate the importance of critical thinking and dialectical reasoning in philosophical inquiry.