The influential philosopher best known for their works on ethics and morality is Immanuel Kant. His critical philosophy laid foundational principles in ethics, notably through his concepts of the Categorical Imperative and the importance of duty. Kant emphasized that moral actions must be universally applicable and grounded in reason rather than consequences. In works like "Groundwork for the Metaphysics of Morals" and "Critique of Practical Reason," he explored the relationship between freedom, autonomy, and ethical principles, significantly impacting Western philosophy and shaping subsequent moral theories.