Immanuel Kant was an influential German philosopher of the 18th century. He is known for his work in metaphysics, epistemology, ethics, and aesthetics. Kant's most famous work is the "Critique of Pure Reason," in which he explores the nature of human knowledge and the limits of reason. He also developed the concept of the categorical imperative as a moral principle and made significant contributions to the fields of ethics and political philosophy. Kant's ideas have had a profound impact on modern philosophy and continue to be studied and debated by scholars around the world.