Immanuel Kant was an influential German philosopher in the 18th century, known for his work in ethics and metaphysics. He introduced the idea of the categorical imperative, which suggests that moral actions should be based on universal principles that everyone can follow. This means that we should act in ways that could be applied as a rule for everyone, promoting fairness and justice. Kant also explored the relationship between knowledge and experience in his book, Critique of Pure Reason. He argued that our understanding of the world is shaped by both our senses and our innate concepts. This idea laid the groundwork for modern philosophy and influenced many thinkers after him.