Immanuel Kant was a German philosopher who lived from 1724 to 1804 and became one of the most influential thinkers in Western philosophy. He is best known for his work on ethics, metaphysics, and epistemology, particularly his "Critique of Pure Reason" which attempted to synthesize rationalist and empiricist approaches to understanding human knowledge and experience. Kant's ethical theory centered on the idea of the "categorical imperative," which proposed that moral actions should be based on universal principles rather than consequences.